This is tar.info, produced by makeinfo version 6.7 from tar.texi.

This manual is for GNU ‘tar’ (version 1.35, 10 July 2023), which creates
and extracts files from archives.

   Copyright © 1992, 1994–1997, 1999–2001, 2003–2017, 2021–2023 Free
Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.3 or any later version published by the Free Software
     Foundation; with the Invariant Sections being “GNU General Public
     License”, with the Front-Cover Texts being “A GNU Manual”, and with
     the Back-Cover Texts as in (a) below.  A copy of the license is
     included in the section entitled “GNU Free Documentation License”.

     (a) The FSF’s Back-Cover Text is: “You have the freedom to copy and
     modify this GNU manual.”
INFO-DIR-SECTION Archiving
START-INFO-DIR-ENTRY
* Tar: (tar).                   Making tape (or disk) archives.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* tar: (tar)tar invocation.                     Invoking GNU ‘tar’.
END-INFO-DIR-ENTRY


File: tar.info,  Node: Top,  Next: Introduction,  Up: (dir)

GNU tar: an archiver tool
*************************

This manual is for GNU ‘tar’ (version 1.35, 10 July 2023), which creates
and extracts files from archives.

   Copyright © 1992, 1994–1997, 1999–2001, 2003–2017, 2021–2023 Free
Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.3 or any later version published by the Free Software
     Foundation; with the Invariant Sections being “GNU General Public
     License”, with the Front-Cover Texts being “A GNU Manual”, and with
     the Back-Cover Texts as in (a) below.  A copy of the license is
     included in the section entitled “GNU Free Documentation License”.

     (a) The FSF’s Back-Cover Text is: “You have the freedom to copy and
     modify this GNU manual.”

   The first part of this master menu lists the major nodes in this Info
document.  The rest of the menu lists all the lower level nodes.

* Menu:

* Introduction::
* Tutorial::
* tar invocation::
* operations::
* Backups::
* Choosing::
* Date input formats::
* Formats::
* Media::
* Reliability and security::

Appendices

* Changes::
* Recipes:: Frequently used tar recipes
* Configuring Help Summary::
* Fixing Snapshot Files::
* Tar Internals::
* Genfile::
* GNU Free Documentation License::
* Index of Command Line Options::
* Index::

 — The Detailed Node Listing —

Introduction

* Book Contents::               What this Book Contains
* Definitions::                 Some Definitions
* What tar Does::               What ‘tar’ Does
* Naming tar Archives::         How ‘tar’ Archives are Named
* Authors::                     GNU ‘tar’ Authors
* Reports::                     Reporting bugs or suggestions

Tutorial Introduction to ‘tar’

* assumptions::
* stylistic conventions::
* basic tar options::           Basic ‘tar’ Operations and Options
* frequent operations::
* Two Frequent Options::
* create::                      How to Create Archives
* list::                        How to List Archives
* extract::                     How to Extract Members from an Archive
* going further::

Two Frequently Used Options

* file tutorial::
* verbose tutorial::
* help tutorial::

How to Create Archives

* prepare for examples::
* Creating the archive::
* create verbose::
* short create::
* create dir::

How to List Archives

* list dir::

How to Extract Members from an Archive

* extracting archives::
* extracting files::
* extract dir::
* extracting untrusted archives::
* failing commands::

Invoking GNU ‘tar’

* Synopsis::
* using tar options::
* Styles::
* All Options::           All ‘tar’ Options.
* help::                  Where to Get Help.
* defaults::              What are the Default Values.
* verbose::               Checking ‘tar’ progress.
* checkpoints::           Checkpoints.
* warnings::              Controlling Warning Messages.
* interactive::           Asking for Confirmation During Operations.
* external::              Running External Commands.

The Three Option Styles

* Long Options::                Long Option Style
* Short Options::               Short Option Style
* Old Options::                 Old Option Style
* Mixing::                      Mixing Option Styles

All ‘tar’ Options

* Operation Summary::
* Option Summary::
* Short Option Summary::
* Position-Sensitive Options::

Controlling Warning Messages

* General Warnings::  Keywords applicable for ‘tar --create’.
* Archive Creation Warnings:: Keywords applicable for ‘tar --create’.
* Archive Extraction Warnings:: Keywords applicable for ‘tar --extract’.
* Incremental Extraction Warnings:: Keywords controlling incremental extraction.
* Warning Classes:: Convenience keywords control multiple warnings.
* Warning Defaults:: Default settings for warnings.

GNU ‘tar’ Operations

* Basic tar::
* Advanced tar::
* create options::
* extract options::
* backup::
* looking ahead::

Advanced GNU ‘tar’ Operations

* Operations::
* append::
* update::
* concatenate::
* delete::
* compare::

How to Add Files to Existing Archives: ‘--append’

* appending files::             Appending Files to an Archive
* multiple::

Updating an Archive

* how to update::

Options Used by ‘--create’

* override::                  Overriding File Metadata.
* Extended File Attributes::
* Ignore Failed Read::

Options Used by ‘--extract’

* Reading::                     Options to Help Read Archives
* Writing::                     Changing How ‘tar’ Writes Files
* Scarce::                      Coping with Scarce Resources

Options to Help Read Archives

* read full records::
* Ignore Zeros::

Changing How ‘tar’ Writes Files

* Dealing with Old Files::
* Overwrite Old Files::
* Keep Old Files::
* Keep Newer Files::
* Unlink First::
* Recursive Unlink::
* Data Modification Times::
* Setting Access Permissions::
* Directory Modification Times and Permissions::
* Writing to Standard Output::
* Writing to an External Program::
* remove files::

Coping with Scarce Resources

* Starting File::
* Same Order::

Performing Backups and Restoring Files

* Full Dumps::                  Using ‘tar’ to Perform Full Dumps
* Incremental Dumps::           Using ‘tar’ to Perform Incremental Dumps
* Backup Levels::               Levels of Backups
* Backup Parameters::           Setting Parameters for Backups and Restoration
* Scripted Backups::            Using the Backup Scripts
* Scripted Restoration::        Using the Restore Script

Setting Parameters for Backups and Restoration

* General-Purpose Variables::
* Magnetic Tape Control::
* User Hooks::
* backup-specs example::        An Example Text of ‘Backup-specs’

Choosing Files and Names for ‘tar’

* file::                        Choosing the Archive’s Name
* Selecting Archive Members::
* files::                       Reading Names from a File
* exclude::                     Excluding Some Files
* wildcards::                   Wildcards Patterns and Matching
* quoting styles::              Ways of Quoting Special Characters in Names
* transform::                   Modifying File and Member Names
* after::                       Operating Only on New Files
* recurse::                     Descending into Directories
* one::                         Crossing File System Boundaries

Reading Names from a File

* nul::

Excluding Some Files

* problems with exclude::

Wildcards Patterns and Matching

* controlling pattern-matching::

Crossing File System Boundaries

* directory::                   Changing Directory
* absolute::                    Absolute File Names

Date input formats

* General date syntax::          Common rules
* Calendar date items::          21 Jul 2020
* Time of day items::            9:20pm
* Time zone items::              UTC, -0700, +0900, ...
* Combined date and time of day items:: 2020-07-21T20:02:00,000000-0400
* Day of week items::            Monday and others
* Relative items in date strings:: next tuesday, 2 years ago
* Pure numbers in date strings:: 20200721, 1440
* Seconds since the Epoch::      @1595289600
* Specifying time zone rules::   TZ="America/New_York", TZ="UTC0"
* Authors of parse_datetime::    Bellovin, Eggert, Salz, Berets, et al.

Controlling the Archive Format

* Compression::                 Using Less Space through Compression
* Attributes::                  Handling File Attributes
* Portability::                 Making ‘tar’ Archives More Portable
* cpio::                        Comparison of ‘tar’ and ‘cpio’

Using Less Space through Compression

* gzip::                        Creating and Reading Compressed Archives
* sparse::                      Archiving Sparse Files

Creating and Reading Compressed Archives

* lbzip2::  Using lbzip2 with GNU ‘tar’.

Making ‘tar’ Archives More Portable

* Portable Names::              Portable Names
* dereference::                 Symbolic Links
* hard links::                  Hard Links
* old::                         Old V7 Archives
* ustar::                       Ustar Archives
* gnu::                         GNU and old GNU format archives.
* posix::                       POSIX archives
* Checksumming::                Checksumming Problems
* Large or Negative Values::    Large files, negative time stamps, etc.
* Other Tars::                  How to Extract GNU-Specific Data Using
                                Other ‘tar’ Implementations

GNU ‘tar’ and POSIX ‘tar’

* PAX keywords:: Controlling Extended Header Keywords.

How to Extract GNU-Specific Data Using Other ‘tar’ Implementations

* Split Recovery::       Members Split Between Volumes
* Sparse Recovery::      Sparse Members

Tapes and Other Archive Media

* Device::                      Device selection and switching
* Remote Tape Server::
* Common Problems and Solutions::
* Blocking::                    Blocking
* Many::                        Many archives on one tape
* Using Multiple Tapes::        Using Multiple Tapes
* label::                       Including a Label in the Archive
* verify::
* Write Protection::

Blocking

* Format Variations::           Format Variations
* Blocking Factor::             The Blocking Factor of an Archive

Many Archives on One Tape

* Tape Positioning::            Tape Positions and Tape Marks
* mt::                          The ‘mt’ Utility

Using Multiple Tapes

* Multi-Volume Archives::       Archives Longer than One Tape or Disk
* Tape Files::                  Tape Files
* Tarcat::                      Concatenate Volumes into a Single Archive


Reliability and Security

* Reliability::
* Security::

Reliability

* Permissions problems::
* Data corruption and repair::
* Race conditions::

Security

* Privacy::
* Integrity::
* Live untrusted data::
* Security rules of thumb::

Recipes

* copy directory hierarchy::
* intermediate directories::

Tar Internals

* Standard::           Basic Tar Format
* Extensions::         GNU Extensions to the Archive Format
* Sparse Formats::     Storing Sparse Files
* Snapshot Files::
* Dumpdir::

Storing Sparse Files

* Old GNU Format::
* PAX 0::                PAX Format, Versions 0.0 and 0.1
* PAX 1::                PAX Format, Version 1.0

Genfile

* Generate Mode::     File Generation Mode.
* Status Mode::       File Status Mode.
* Exec Mode::         Synchronous Execution mode.

Copying This Manual

* GNU Free Documentation License::  License for copying this manual.



File: tar.info,  Node: Introduction,  Next: Tutorial,  Prev: Top,  Up: Top

1 Introduction
**************

GNU ‘tar’ creates and manipulates “archives” which are actually
collections of many other files; the program provides users with an
organized and systematic method for controlling a large amount of data.
The name “tar” originally came from the phrase “Tape ARchive”, but
archives need not (and these days, typically do not) reside on tapes.

* Menu:

* Book Contents::               What this Book Contains
* Definitions::                 Some Definitions
* What tar Does::               What ‘tar’ Does
* Naming tar Archives::         How ‘tar’ Archives are Named
* Authors::                     GNU ‘tar’ Authors
* Reports::                     Reporting bugs or suggestions


File: tar.info,  Node: Book Contents,  Next: Definitions,  Up: Introduction

1.1 What this Book Contains
===========================

The first part of this chapter introduces you to various terms that will
recur throughout the book.  It also tells you who has worked on GNU
‘tar’ and its documentation, and where you should send bug reports or
comments.

   The second chapter is a tutorial (*note Tutorial::) which provides a
gentle introduction for people who are new to using ‘tar’.  It is meant
to be self-contained, not requiring any reading from subsequent chapters
to make sense.  It moves from topic to topic in a logical, progressive
order, building on information already explained.

   Although the tutorial is paced and structured to allow beginners to
learn how to use ‘tar’, it is not intended solely for beginners.  The
tutorial explains how to use the three most frequently used operations
(‘create’, ‘list’, and ‘extract’) as well as two frequently used options
(‘file’ and ‘verbose’).  The other chapters do not refer to the tutorial
frequently; however, if a section discusses something which is a complex
variant of a basic concept, there may be a cross-reference to that basic
concept.  (The entire book, including the tutorial, assumes that the
reader understands some basic concepts of using a Unix-type operating
system; *note Tutorial::.)

   The third chapter presents the remaining five operations, and
information about using ‘tar’ options and option syntax.

   The other chapters are meant to be used as a reference.  Each chapter
presents everything that needs to be said about a specific topic.

   One of the chapters (*note Date input formats::) exists in its
entirety in other GNU manuals, and is mostly self-contained.  In
addition, one section of this manual (*note Standard::) contains a big
quote which is taken directly from ‘tar’ sources.

   In general, we give both long and short (abbreviated) option names at
least once in each section where the relevant option is covered, so that
novice readers will become familiar with both styles.  (A few options
have no short versions, and the relevant sections will indicate this.)


File: tar.info,  Node: Definitions,  Next: What tar Does,  Prev: Book Contents,  Up: Introduction

1.2 Some Definitions
====================

The ‘tar’ program is used to create and manipulate ‘tar’ archives.  An
“archive” is a single file which contains the contents of many files,
while still identifying the names of the files, their owner(s), and so
forth.  (In addition, archives record access permissions, user and
group, size in bytes, and data modification time.  Some archives also
record the file names in each archived directory, as well as other file
and directory information.)  You can use ‘tar’ to “create” a new archive
in a specified directory.

   The files inside an archive are called “members”.  Within this
manual, we use the term “file” to refer only to files accessible in the
normal ways (by ‘ls’, ‘cat’, and so forth), and the term “member” to
refer only to the members of an archive.  Similarly, a “file name” is
the name of a file, as it resides in the file system, and a “member
name” is the name of an archive member within the archive.

   The term “extraction” refers to the process of copying an archive
member (or multiple members) into a file in the file system.  Extracting
all the members of an archive is often called “extracting the archive”.
The term “unpack” can also be used to refer to the extraction of many or
all the members of an archive.  Extracting an archive does not destroy
the archive’s structure, just as creating an archive does not destroy
the copies of the files that exist outside of the archive.  You may also
“list” the members in a given archive (this is often thought of as
“printing” them to the standard output, or the command line), or
“append” members to a pre-existing archive.  All of these operations can
be performed using ‘tar’.


File: tar.info,  Node: What tar Does,  Next: Naming tar Archives,  Prev: Definitions,  Up: Introduction

1.3 What ‘tar’ Does
===================

The ‘tar’ program provides the ability to create ‘tar’ archives, as well
as various other kinds of manipulation.  For example, you can use ‘tar’
on previously created archives to extract files, to store additional
files, or to update or list files which were already stored.

   Initially, ‘tar’ archives were used to store files conveniently on
magnetic tape.  The name ‘tar’ comes from this use; it stands for ‘t’ape
‘ar’chiver.  Despite the utility’s name, ‘tar’ can direct its output to
available devices, files, or other programs (using pipes).  ‘tar’ may
even access remote devices or files (as archives).

   You can use ‘tar’ archives in many ways.  We want to stress a few of
them: storage, backup, and transportation.

Storage
     Often, ‘tar’ archives are used to store related files for
     convenient file transfer over a network.  For example, the GNU
     Project distributes its software bundled into ‘tar’ archives, so
     that all the files relating to a particular program (or set of
     related programs) can be transferred as a single unit.

     A magnetic tape can store several files in sequence.  However, the
     tape has no names for these files; it only knows their relative
     position on the tape.  One way to store several files on one tape
     and retain their names is by creating a ‘tar’ archive.  Even when
     the basic transfer mechanism can keep track of names, as FTP can,
     the nuisance of handling multiple files, directories, and multiple
     links makes ‘tar’ archives useful.

     Archive files are also used for long-term storage.  You can think
     of this as transportation from the present into the future.  (It is
     a science-fiction idiom that you can move through time as well as
     in space; the idea here is that ‘tar’ can be used to move archives
     in all dimensions, even time!)

Backup
     Because the archive created by ‘tar’ is capable of preserving file
     information and directory structure, ‘tar’ is commonly used for
     performing full and incremental backups of disks.  A backup puts a
     collection of files (possibly pertaining to many users and
     projects) together on a disk or a tape.  This guards against
     accidental destruction of the information in those files.  GNU
     ‘tar’ has special features that allow it to be used to make
     incremental and full dumps of all the files in a file system.

Transportation
     You can create an archive on one system, transfer it to another
     system, and extract the contents there.  This allows you to
     transport a group of files from one system to another.


File: tar.info,  Node: Naming tar Archives,  Next: Authors,  Prev: What tar Does,  Up: Introduction

1.4 How ‘tar’ Archives are Named
================================

Conventionally, ‘tar’ archives are given names ending with ‘.tar’.  This
is not necessary for ‘tar’ to operate properly, but this manual follows
that convention in order to accustom readers to it and to make examples
more clear.

   Often, people refer to ‘tar’ archives as “‘tar’ files,” and archive
members as “files” or “entries”.  For people familiar with the operation
of ‘tar’, this causes no difficulty.  However, in this manual, we
consistently refer to “archives” and “archive members” to make learning
to use ‘tar’ easier for novice users.


File: tar.info,  Node: Authors,  Next: Reports,  Prev: Naming tar Archives,  Up: Introduction

1.5 GNU ‘tar’ Authors
=====================

GNU ‘tar’ was originally written by John Gilmore, and modified by many
people.  The GNU enhancements were written by Jay Fenlason, then Joy
Kendall, and the whole package has been further maintained by Thomas
Bushnell, n/BSG, François Pinard, Paul Eggert, and finally Sergey
Poznyakoff with the help of numerous and kind users.

   We wish to stress that ‘tar’ is a collective work, and owes much to
all those people who reported problems, offered solutions and other
insights, or shared their thoughts and suggestions.  An impressive, yet
partial list of those contributors can be found in the ‘THANKS’ file
from the GNU ‘tar’ distribution.

   Jay Fenlason put together a draft of a GNU ‘tar’ manual, borrowing
notes from the original man page from John Gilmore.  This was withdrawn
in version 1.11.  Thomas Bushnell, n/BSG and Amy Gorin worked on a
tutorial and manual for GNU ‘tar’.  François Pinard put version 1.11.8
of the manual together by taking information from all these sources and
merging them.  Melissa Weisshaus finally edited and redesigned the book
to create version 1.12.  The book for versions from 1.14 up to 1.35 were
edited by the current maintainer, Sergey Poznyakoff.

   For version 1.12, Daniel Hagerty contributed a great deal of
technical consulting.  In particular, he is the primary author of *note
Backups::.

   In July, 2003 GNU ‘tar’ was put on CVS at savannah.gnu.org (see
<https://savannah.gnu.org/projects/tar>), and active development and
maintenance work has started again.  Currently GNU ‘tar’ is being
maintained by Paul Eggert, Sergey Poznyakoff and Jeff Bailey.

   Support for POSIX archives was added by Sergey Poznyakoff.


File: tar.info,  Node: Reports,  Prev: Authors,  Up: Introduction

1.6 Reporting bugs or suggestions
=================================

If you find problems or have suggestions about this program or manual,
please report them to ‘bug-tar@gnu.org’.

   When reporting a bug, please be sure to include as much detail as
possible, in order to reproduce it.


File: tar.info,  Node: Tutorial,  Next: tar invocation,  Prev: Introduction,  Up: Top

2 Tutorial Introduction to ‘tar’
********************************

This chapter guides you through some basic examples of three ‘tar’
operations: ‘--create’, ‘--list’, and ‘--extract’.  If you already know
how to use some other version of ‘tar’, then you may not need to read
this chapter.  This chapter omits most complicated details about how
‘tar’ works.

* Menu:

* assumptions::
* stylistic conventions::
* basic tar options::           Basic ‘tar’ Operations and Options
* frequent operations::
* Two Frequent Options::
* create::                      How to Create Archives
* list::                        How to List Archives
* extract::                     How to Extract Members from an Archive
* going further::


File: tar.info,  Node: assumptions,  Next: stylistic conventions,  Up: Tutorial

2.1 Assumptions this Tutorial Makes
===================================

This chapter is paced to allow beginners to learn about ‘tar’ slowly.
At the same time, we will try to cover all the basic aspects of these
three operations.  In order to accomplish both of these tasks, we have
made certain assumptions about your knowledge before reading this
manual, and the hardware you will be using:

   • Before you start to work through this tutorial, you should
     understand what the terms “archive” and “archive member” mean
     (*note Definitions::).  In addition, you should understand
     something about how Unix-type operating systems work, and you
     should know how to use some basic utilities.  For example, you
     should know how to create, list, copy, rename, edit, and delete
     files and directories; how to change between directories; and how
     to figure out where you are in the file system.  You should have
     some basic understanding of directory structure and how files are
     named according to which directory they are in.  You should
     understand concepts such as standard output and standard input,
     what various definitions of the term ‘argument’ mean, and the
     differences between relative and absolute file names.

   • This manual assumes that you are working from your own home
     directory (unless we state otherwise).  In this tutorial, you will
     create a directory to practice ‘tar’ commands in.  When we show
     file names, we will assume that those names are relative to your
     home directory.  For example, my home directory is
     ‘/home/fsf/melissa’.  All of my examples are in a subdirectory of
     the directory named by that file name; the subdirectory is called
     ‘practice’.

   • In general, we show examples of archives which exist on (or can be
     written to, or worked with from) a directory on a hard disk.  In
     most cases, you could write those archives to, or work with them on
     any other device, such as a tape drive.  However, some of the later
     examples in the tutorial and next chapter will not work on tape
     drives.  Additionally, working with tapes is much more complicated
     than working with hard disks.  For these reasons, the tutorial does
     not cover working with tape drives.  *Note Media::, for complete
     information on using ‘tar’ archives with tape drives.


File: tar.info,  Node: stylistic conventions,  Next: basic tar options,  Prev: assumptions,  Up: Tutorial

2.2 Stylistic Conventions
=========================

In the examples, ‘$’ represents a typical shell prompt.  It precedes
lines you should type; to make this more clear, those lines are shown in
‘this font’, as opposed to lines which represent the computer’s
response; those lines are shown in ‘this font’, or sometimes ‘like
this’.


File: tar.info,  Node: basic tar options,  Next: frequent operations,  Prev: stylistic conventions,  Up: Tutorial

2.3 Basic ‘tar’ Operations and Options
======================================

‘tar’ can take a wide variety of arguments which specify and define the
actions it will have on the particular set of files or the archive.  The
main types of arguments to ‘tar’ fall into one of two classes:
operations, and options.

   Some arguments fall into a class called “operations”; exactly one of
these is both allowed and required for any instance of using ‘tar’; you
may _not_ specify more than one.  People sometimes speak of “operating
modes”.  You are in a particular operating mode when you have specified
the operation which specifies it; there are eight operations in total,
and thus there are eight operating modes.

   The other arguments fall into the class known as “options”.  You are
not required to specify any options, and you are allowed to specify more
than one at a time (depending on the way you are using ‘tar’ at that
time).  Some options are used so frequently, and are so useful for
helping you type commands more carefully that they are effectively
“required”.  We will discuss them in this chapter.

   You can write most of the ‘tar’ operations and options in any of
three forms: long (mnemonic) form, short form, and old style.  Some of
the operations and options have no short or “old” forms; however, the
operations and options which we will cover in this tutorial have
corresponding abbreviations.  We will indicate those abbreviations
appropriately to get you used to seeing them.  Note, that the “old
style” option forms exist in GNU ‘tar’ for compatibility with Unix
‘tar’.  In this book we present a full discussion of this way of writing
options and operations (*note Old Options::), and we discuss the other
two styles of writing options (*Note Long Options::, and *note Short
Options::).

   In the examples and in the text of this tutorial, we usually use the
long forms of operations and options; but the “short” forms produce the
same result and can make typing long ‘tar’ commands easier.  For
example, instead of typing

     tar --create --verbose --file=afiles.tar apple angst aspic

you can type
     tar -c -v -f afiles.tar apple angst aspic

or even
     tar -cvf afiles.tar apple angst aspic

For more information on option syntax, see *note Advanced tar::.  In
discussions in the text, when we name an option by its long form, we
also give the corresponding short option in parentheses.

   The term, “option”, can be confusing at times, since “operations” are
often lumped in with the actual, _optional_ “options” in certain general
class statements.  For example, we just talked about “short and long
forms of options and operations”.  However, experienced ‘tar’ users
often refer to these by shorthand terms such as, “short and long
options”.  This term assumes that the “operations” are included, also.
Context will help you determine which definition of “options” to use.

   Similarly, the term “command” can be confusing, as it is often used
in two different ways.  People sometimes refer to ‘tar’ “commands”.  A
‘tar’ “command” is the entire command line of user input which tells
‘tar’ what to do — including the operation, options, and any arguments
(file names, pipes, other commands, etc.).  However, you will also
sometimes hear the term “the ‘tar’ command”.  When the word “command” is
used specifically like this, a person is usually referring to the ‘tar’
_operation_, not the whole line.  Again, use context to figure out which
of the meanings the speaker intends.


File: tar.info,  Node: frequent operations,  Next: Two Frequent Options,  Prev: basic tar options,  Up: Tutorial

2.4 The Three Most Frequently Used Operations
=============================================

Here are the three most frequently used operations (both short and long
forms), as well as a brief description of their meanings.  The rest of
this chapter will cover how to use these operations in detail.  We will
present the rest of the operations in the next chapter.

‘--create’
‘-c’
     Create a new ‘tar’ archive.
‘--list’
‘-t’
     List the contents of an archive.
‘--extract’
‘-x’
     Extract one or more members from an archive.


File: tar.info,  Node: Two Frequent Options,  Next: create,  Prev: frequent operations,  Up: Tutorial

2.5 Two Frequently Used Options
===============================

To understand how to run ‘tar’ in the three operating modes listed
previously, you also need to understand how to use two of the options to
‘tar’: ‘--file’ (which takes an archive file as an argument) and
‘--verbose’.  (You are usually not _required_ to specify either of these
options when you run ‘tar’, but they can be very useful in making things
more clear and helping you avoid errors.)

* Menu:

* file tutorial::
* verbose tutorial::
* help tutorial::


File: tar.info,  Node: file tutorial,  Next: verbose tutorial,  Up: Two Frequent Options

The ‘--file’ Option
-------------------

‘--file=ARCHIVE-NAME’
‘-f ARCHIVE-NAME’
     Specify the name of an archive file.

   You can specify an argument for the ‘--file=ARCHIVE-NAME’ (‘-f
ARCHIVE-NAME’) option whenever you use ‘tar’; this option determines the
name of the archive file that ‘tar’ will work on.

   If you don’t specify this argument, then ‘tar’ will examine the
environment variable ‘TAPE’.  If it is set, its value will be used as
the archive name.  Otherwise, ‘tar’ will use the default archive,
determined at compile time.  Usually it is standard output or some
physical tape drive attached to your machine (you can verify what the
default is by running ‘tar --show-defaults’, *note defaults::).  If
there is no tape drive attached, or the default is not meaningful, then
‘tar’ will print an error message.  The error message might look roughly
like one of the following:

     tar: can't open /dev/rmt8 : No such device or address
     tar: can't open /dev/rsmt0 : I/O error

To avoid confusion, we recommend that you always specify an archive file
name by using ‘--file=ARCHIVE-NAME’ (‘-f ARCHIVE-NAME’) when writing
your ‘tar’ commands.  For more information on using the
‘--file=ARCHIVE-NAME’ (‘-f ARCHIVE-NAME’) option, see *note file::.


File: tar.info,  Node: verbose tutorial,  Next: help tutorial,  Prev: file tutorial,  Up: Two Frequent Options

The ‘--verbose’ Option
----------------------

‘--verbose’
‘-v’
     Show the files being worked on as ‘tar’ is running.

   ‘--verbose’ (‘-v’) shows details about the results of running ‘tar’.
This can be especially useful when the results might not be obvious.
For example, if you want to see the progress of ‘tar’ as it writes files
into the archive, you can use the ‘--verbose’ option.  In the beginning,
you may find it useful to use ‘--verbose’ at all times; when you are
more accustomed to ‘tar’, you will likely want to use it at certain
times but not at others.  We will use ‘--verbose’ at times to help make
something clear, and we will give many examples both using and not using
‘--verbose’ to show the differences.

   Each instance of ‘--verbose’ on the command line increases the
verbosity level by one, so if you need more details on the output,
specify it twice.

   When reading archives (‘--list’, ‘--extract’, ‘--diff’), ‘tar’ by
default prints only the names of the members being extracted.  Using
‘--verbose’ will show a full, ‘ls’ style member listing.

   In contrast, when writing archives (‘--create’, ‘--append’,
‘--update’), ‘tar’ does not print file names by default.  So, a single
‘--verbose’ option shows the file names being added to the archive,
while two ‘--verbose’ options enable the full listing.

   For example, to create an archive in verbose mode:

     $ tar -cvf afiles.tar apple angst aspic
     apple
     angst
     aspic

Creating the same archive with the verbosity level 2 could give:

     $ tar -cvvf afiles.tar apple angst aspic
     -rw-r--r-- gray/staff    62373 2006-06-09 12:06 apple
     -rw-r--r-- gray/staff    11481 2006-06-09 12:06 angst
     -rw-r--r-- gray/staff    23152 2006-06-09 12:06 aspic

This works equally well using short or long forms of options.  Using
long forms, you would simply write out the mnemonic form of the option
twice, like this:

     $ tar --create --verbose --verbose ...

Note that you must double the hyphens properly each time.

   Later in the tutorial, we will give examples using
‘--verbose --verbose’.

   The ‘--verbose’ option also enables several “warning messages”, that
tar does not issue otherwise, such as the warning about record size
being used (*note Blocking Factor::), selecting the decompress program
and the like.  If these are of no interest to you, you can suppress them
using the ‘--warning’ option _after_ ‘--verbose’, e.g.:

     $ tar -c -v --warning=no-verbose -f afiles.tar apple angst aspic

   *Note verbose: Warning Classes, for details.

   The full output consists of six fields:

   • File type and permissions in symbolic form.  These are displayed in
     the same format as the first column of ‘ls -l’ output (*note
     format=verbose: (fileutils)What information is listed.).

   • Owner name and group separated by a slash character.  If these data
     are not available (for example, when listing a ‘v7’ format
     archive), numeric ID values are printed instead.

   • Size of the file, in bytes.

   • File modification date in ISO 8601 format.

   • File modification time.

   • File name.  If the name contains any special characters (white
     space, newlines, etc.) these are displayed in an unambiguous form
     using so called “quoting style”.  For the detailed discussion of
     available styles and on how to use them, see *note quoting
     styles::.

     Depending on the file type, the name can be followed by some
     additional information, described in the following table:

     ‘-> LINK-NAME’
          The file or archive member is a “symbolic link” and LINK-NAME
          is the name of file it links to.

     ‘link to LINK-NAME’
          The file or archive member is a “hard link” and LINK-NAME is
          the name of file it links to.

     ‘--Long Link--’
          The archive member is an old GNU format long link.  You will
          normally not encounter this.

     ‘--Long Name--’
          The archive member is an old GNU format long name.  You will
          normally not encounter this.

     ‘--Volume Header--’
          The archive member is a GNU “volume header” (*note Tape
          Files::).

     ‘--Continued at byte N--’
          Encountered only at the beginning of a multi-volume archive
          (*note Using Multiple Tapes::).  This archive member is a
          continuation from the previous volume.  The number N gives the
          offset where the original file was split.

     ‘unknown file type C’
          An archive member of unknown type.  C is the type character
          from the archive header.  If you encounter such a message, it
          means that either your archive contains proprietary member
          types GNU ‘tar’ is not able to handle, or the archive is
          corrupted.

   For example, here is an archive listing containing most of the
special suffixes explained above:

     V--------- 0/0            1536 2006-06-09 13:07 MyVolume--Volume Header--
     -rw-r--r-- gray/staff   456783 2006-06-09 12:06 aspic--Continued at byte 32456--
     -rw-r--r-- gray/staff    62373 2006-06-09 12:06 apple
     lrwxrwxrwx gray/staff        0 2006-06-09 13:01 angst -> apple
     -rw-r--r-- gray/staff    35793 2006-06-09 12:06 blues
     hrw-r--r-- gray/staff        0 2006-06-09 12:06 music link to blues


File: tar.info,  Node: help tutorial,  Prev: verbose tutorial,  Up: Two Frequent Options

Getting Help: Using the ‘--help’ Option
---------------------------------------

‘--help’

     The ‘--help’ option to ‘tar’ prints out a very brief list of all
     operations and option available for the current version of ‘tar’
     available on your system.


File: tar.info,  Node: create,  Next: list,  Prev: Two Frequent Options,  Up: Tutorial

2.6 How to Create Archives
==========================

One of the basic operations of ‘tar’ is ‘--create’ (‘-c’), which you use
to create a ‘tar’ archive.  We will explain ‘--create’ first because, in
order to learn about the other operations, you will find it useful to
have an archive available to practice on.

   To make this easier, in this section you will first create a
directory containing three files.  Then, we will show you how to create
an _archive_ (inside the new directory).  Both the directory, and the
archive are specifically for you to practice on.  The rest of this
chapter and the next chapter will show many examples using this
directory and the files you will create: some of those files may be
other directories and other archives.

   The three files you will archive in this example are called ‘blues’,
‘folk’, and ‘jazz’.  The archive is called ‘collection.tar’.

   This section will proceed slowly, detailing how to use ‘--create’ in
‘verbose’ mode, and showing examples using both short and long forms.
In the rest of the tutorial, and in the examples in the next chapter, we
will proceed at a slightly quicker pace.  This section moves more slowly
to allow beginning users to understand how ‘tar’ works.

* Menu:

* prepare for examples::
* Creating the archive::
* create verbose::
* short create::
* create dir::


File: tar.info,  Node: prepare for examples,  Next: Creating the archive,  Up: create

2.6.1 Preparing a Practice Directory for Examples
-------------------------------------------------

To follow along with this and future examples, create a new directory
called ‘practice’ containing files called ‘blues’, ‘folk’ and ‘jazz’.
The files can contain any information you like: ideally, they should
contain information which relates to their names, and be of different
lengths.  Our examples assume that ‘practice’ is a subdirectory of your
home directory.

   Now ‘cd’ to the directory named ‘practice’; ‘practice’ is now your
“working directory”.  (_Please note_: Although the full file name of
this directory is ‘/HOMEDIR/practice’, in our examples we will refer to
this directory as ‘practice’; the HOMEDIR is presumed.)

   In general, you should check that the files to be archived exist
where you think they do (in the working directory) by running ‘ls’.
Because you just created the directory and the files and have changed to
that directory, you probably don’t need to do that this time.

   It is very important to make sure there isn’t already a file in the
working directory with the archive name you intend to use (in this case,
‘collection.tar’), or that you don’t care about its contents.  Whenever
you use ‘create’, ‘tar’ will erase the current contents of the file
named by ‘--file=ARCHIVE-NAME’ (‘-f ARCHIVE-NAME’) if it exists.  ‘tar’
will not tell you if you are about to overwrite an archive unless you
specify an option which does this (*note backup::, for the information
on how to do so).  To add files to an existing archive, you need to use
a different option, such as ‘--append’ (‘-r’); see *note append:: for
information on how to do this.


File: tar.info,  Node: Creating the archive,  Next: create verbose,  Prev: prepare for examples,  Up: create

2.6.2 Creating the Archive
--------------------------

To place the files ‘blues’, ‘folk’, and ‘jazz’ into an archive named
‘collection.tar’, use the following command:

     $ tar --create --file=collection.tar blues folk jazz

   The order of the arguments is not very important, _when using long
option forms_, however you should always remember to use option as the
first argument to tar.  For example, the following is wrong:

     $ tar blues -c folk -f collection.tar jazz
     tar: -c: Invalid blocking factor
     Try 'tar --help' or 'tar --usage' for more information.

   The error message is produced because ‘tar’ always treats its first
argument as an option (or cluster of options), even if it does not start
with dash.  This is “traditional” or “old option” style, called so
because all implementations of ‘tar’ have used it since the very
inception of the tar archiver in 1970s.  This option style will be
explained later (*note Old Options::), for now just remember to always
place option as the first argument.

   That being said, you could issue the following command:

     $ tar --create folk blues --file=collection.tar jazz

However, you can see that this order is harder to understand; this is
why we will list the arguments in the order that makes the commands
easiest to understand (and we encourage you to do the same when you use
‘tar’, to avoid errors).

   Note that the sequence ‘--file=collection.tar’ is considered to be
_one_ argument.  If you substituted any other string of characters for
‘collection.tar’, then that string would become the name of the archive
file you create.

   The order of the options becomes more important when you begin to use
short forms.  With short forms, if you type commands in the wrong order
(even if you type them correctly in all other ways), you may end up with
results you don’t expect.  For this reason, it is a good idea to get
into the habit of typing options in the order that makes inherent sense.
*Note short create::, for more information on this.

   In this example, you type the command as shown above: ‘--create’ is
the operation which creates the new archive (‘collection.tar’), and
‘--file’ is the option which lets you give it the name you chose.  The
files, ‘blues’, ‘folk’, and ‘jazz’, are now members of the archive,
‘collection.tar’ (they are “file name arguments” to the ‘--create’
operation.  *Note Choosing::, for the detailed discussion on these.)
Now that they are in the archive, they are called _archive members_, not
files.  (*note members: Definitions.).

   When you create an archive, you _must_ specify which files you want
placed in the archive.  If you do not specify any archive members, GNU
‘tar’ will complain.

   If you now list the contents of the working directory (‘ls’), you
will find the archive file listed as well as the files you saw
previously:

     blues   folk   jazz   collection.tar

Creating the archive ‘collection.tar’ did not destroy the copies of the
files in the directory.

   Keep in mind that if you don’t indicate an operation, ‘tar’ will not
run and will prompt you for one.  If you don’t name any files, ‘tar’
will complain.  You must have write access to the working directory, or
else you will not be able to create an archive in that directory.

   _Caution_: Do not attempt to use ‘--create’ (‘-c’) to add files to an
existing archive; it will delete the archive and write a new one.  Use
‘--append’ (‘-r’) instead.  *Note append::.


File: tar.info,  Node: create verbose,  Next: short create,  Prev: Creating the archive,  Up: create

2.6.3 Running ‘--create’ with ‘--verbose’
-----------------------------------------

If you include the ‘--verbose’ (‘-v’) option on the command line, ‘tar’
will list the files it is acting on as it is working.  In verbose mode,
the ‘create’ example above would appear as:

     $ tar --create --verbose --file=collection.tar blues folk jazz
     blues
     folk
     jazz

   This example is just like the example we showed which did not use
‘--verbose’, except that ‘tar’ generated three output lines.

   In the rest of the examples in this chapter, we will frequently use
‘verbose’ mode so we can show actions or ‘tar’ responses that you would
otherwise not see, and which are important for you to understand.


File: tar.info,  Node: short create,  Next: create dir,  Prev: create verbose,  Up: create

2.6.4 Short Forms with ‘create’
-------------------------------

As we said before, the ‘--create’ (‘-c’) operation is one of the most
basic uses of ‘tar’, and you will use it countless times.  Eventually,
you will probably want to use abbreviated (or “short”) forms of options.
A full discussion of the three different forms that options can take
appears in *note Styles::; for now, here is what the previous example
(including the ‘--verbose’ (‘-v’) option) looks like using short option
forms:

     $ tar -cvf collection.tar blues folk jazz
     blues
     folk
     jazz

As you can see, the system responds the same no matter whether you use
long or short option forms.

   One difference between using short and long option forms is that,
although the exact placement of arguments following options is no more
specific when using short forms, it is easier to become confused and
make a mistake when using short forms.  For example, suppose you
attempted the above example in the following way:

     $ tar -cfv collection.tar blues folk jazz

In this case, ‘tar’ will make an archive file called ‘v’, containing the
files ‘blues’, ‘folk’, and ‘jazz’, because the ‘v’ is the closest “file
name” to the ‘-f’ option, and is thus taken to be the chosen archive
file name.  ‘tar’ will try to add a file called ‘collection.tar’ to the
‘v’ archive file; if the file ‘collection.tar’ did not already exist,
‘tar’ will report an error indicating that this file does not exist.  If
the file ‘collection.tar’ does already exist (e.g., from a previous
command you may have run), then ‘tar’ will add this file to the archive.
Because the ‘-v’ option did not get registered, ‘tar’ will not run under
‘verbose’ mode, and will not report its progress.

   The end result is that you may be quite confused about what happened,
and possibly overwrite a file.  To illustrate this further, we will show
you how an example we showed previously would look using short forms.

   This example,

     $ tar --create folk blues --file=collection.tar jazz

is confusing as it is.  It becomes even more so when using short forms:

     $ tar -c folk blues -f collection.tar jazz

It would be very easy to put the wrong string of characters immediately
following the ‘-f’, but doing that could sacrifice valuable data.

   For this reason, we recommend that you pay very careful attention to
the order of options and placement of file and archive names, especially
when using short option forms.  Not having the option name written out
mnemonically can affect how well you remember which option does what,
and therefore where different names have to be placed.


File: tar.info,  Node: create dir,  Prev: short create,  Up: create

2.6.5 Archiving Directories
---------------------------

You can archive a directory by specifying its directory name as a file
name argument to ‘tar’.  The files in the directory will be archived
relative to the working directory, and the directory will be re-created
along with its contents when the archive is extracted.

   To archive a directory, first move to its superior directory.  If you
have followed the previous instructions in this tutorial, you should
type:

     $ cd ..
     $

This will put you into the directory which contains ‘practice’, i.e.,
your home directory.  Once in the superior directory, you can specify
the subdirectory, ‘practice’, as a file name argument.  To store
‘practice’ in the new archive file ‘music.tar’, type:

     $ tar --create --verbose --file=music.tar practice

‘tar’ should output:

     practice/
     practice/blues
     practice/folk
     practice/jazz
     practice/collection.tar

   Note that the archive thus created is not in the subdirectory
‘practice’, but rather in the current working directory—the directory
from which ‘tar’ was invoked.  Before trying to archive a directory from
its superior directory, you should make sure you have write access to
the superior directory itself, not only the directory you are trying
archive with ‘tar’.  For example, you will probably not be able to store
your home directory in an archive by invoking ‘tar’ from the root
directory; *Note absolute::.  (Note also that ‘collection.tar’, the
original archive file, has itself been archived.  ‘tar’ will accept any
file as a file to be archived, regardless of its content.  When
‘music.tar’ is extracted, the archive file ‘collection.tar’ will be
re-written into the file system).

   If you give ‘tar’ a command such as

     $ tar --create --file=foo.tar .

‘tar’ will report ‘tar: ./foo.tar is the archive; not dumped’.  This
happens because ‘tar’ creates the archive ‘foo.tar’ in the current
directory before putting any files into it.  Then, when ‘tar’ attempts
to add all the files in the directory ‘.’ to the archive, it notices
that the file ‘./foo.tar’ is the same as the archive ‘foo.tar’, and
skips it.  (It makes no sense to put an archive into itself.)  GNU ‘tar’
will continue in this case, and create the archive normally, except for
the exclusion of that one file.  (_Please note:_ Other implementations
of ‘tar’ may not be so clever; they will enter an infinite loop when
this happens, so you should not depend on this behavior unless you are
certain you are running GNU ‘tar’.  In general, it is wise to always
place the archive outside of the directory being dumped.)


File: tar.info,  Node: list,  Next: extract,  Prev: create,  Up: Tutorial

2.7 How to List Archives
========================

Frequently, you will find yourself wanting to determine exactly what a
particular archive contains.  You can use the ‘--list’ (‘-t’) operation
to get the member names as they currently appear in the archive, as well
as various attributes of the files at the time they were archived.  For
example, assuming ‘practice’ is your working directory, you can examine
the archive ‘collection.tar’ that you created in the last section with
the command,

     $ tar --list --file=collection.tar

The output of ‘tar’ would then be:

     blues
     folk
     jazz

Be sure to use a ‘--file=ARCHIVE-NAME’ (‘-f ARCHIVE-NAME’) option just
as with ‘--create’ (‘-c’) to specify the name of the archive.

   You can specify one or more individual member names as arguments when
using ‘list’.  In this case, ‘tar’ will only list the names of members
you identify.  For example, ‘tar --list --file=collection.tar folk’
would only print ‘folk’:

     $ tar --list --file=collection.tar folk
     folk

   If you use the ‘--verbose’ (‘-v’) option with ‘--list’, then ‘tar’
will print out a listing reminiscent of ‘ls -l’, showing owner, file
size, and so forth.  This output is described in detail in *note verbose
member listing::.

   If you had used ‘--verbose’ (‘-v’) mode, the example above would look
like:

     $ tar --list --verbose --file=collection.tar folk
     -rw-r--r-- myself/user      62 1990-05-23 10:55 folk

   It is important to notice that the output of ‘tar --list --verbose’
does not necessarily match that produced by ‘tar --create --verbose’
while creating the archive.  It is because GNU ‘tar’, unless told
explicitly not to do so, removes some directory prefixes from file names
before storing them in the archive (*Note absolute::, for more
information).  In other words, in verbose mode GNU ‘tar’ shows “file
names” when creating an archive and “member names” when listing it.
Consider this example, run from your home directory:

     $ tar --create --verbose --file practice.tar ~/practice
     tar: Removing leading '/' from member names
     /home/myself/practice/
     /home/myself/practice/blues
     /home/myself/practice/folk
     /home/myself/practice/jazz
     /home/myself/practice/collection.tar
     $ tar --list --file practice.tar
     home/myself/practice/
     home/myself/practice/blues
     home/myself/practice/folk
     home/myself/practice/jazz
     home/myself/practice/collection.tar

   This default behavior can sometimes be inconvenient.  You can force
GNU ‘tar’ show member names when creating archive by supplying
‘--show-stored-names’ option.

‘--show-stored-names’
     Print member (as opposed to _file_) names when creating the
     archive.

   With this option, both commands produce the same output:

     $ tar --create --verbose --show-stored-names \
                --file practice.tar ~/practice
     tar: Removing leading '/' from member names
     home/myself/practice/
     home/myself/practice/blues
     home/myself/practice/folk
     home/myself/practice/jazz
     home/myself/practice/collection.tar
     $ tar --list --file practice.tar
     home/myself/practice/
     home/myself/practice/blues
     home/myself/practice/folk
     home/myself/practice/jazz
     home/myself/practice/collection.tar

   Since ‘tar’ preserves file names, those you wish to list must be
specified as they appear in the archive (i.e., relative to the directory
from which the archive was created).  Continuing the example above:

     $ tar --list --file=practice.tar folk
     tar: folk: Not found in archive
     tar: Exiting with failure status due to previous errors

   the error message is produced because there is no member named
‘folk’, only one named ‘home/myself/folk’.

   If you are not sure of the exact file name, use “globbing patterns”,
for example:

     $ tar --list --file=practice.tar --wildcards '*/folk'
     home/myself/practice/folk

*Note wildcards::, for a detailed discussion of globbing patterns and
related ‘tar’ command line options.

* Menu:

* list dir::


File: tar.info,  Node: list dir,  Up: list

Listing the Contents of a Stored Directory
------------------------------------------

To get information about the contents of an archived directory, use the
directory name as a file name argument in conjunction with ‘--list’
(‘-t’).  To find out file attributes, include the ‘--verbose’ (‘-v’)
option.

   For example, to find out about files in the directory ‘practice’, in
the archive file ‘music.tar’, type:

     $ tar --list --verbose --file=music.tar practice

   ‘tar’ responds:

     drwxrwxrwx myself/user       0 1990-05-31 21:49 practice/
     -rw-r--r-- myself/user      42 1990-05-21 13:29 practice/blues
     -rw-r--r-- myself/user      62 1990-05-23 10:55 practice/folk
     -rw-r--r-- myself/user      40 1990-05-21 13:30 practice/jazz
     -rw-r--r-- myself/user   10240 1990-05-31 21:49 practice/collection.tar

   When you use a directory name as a file name argument, ‘tar’ acts on
all the files (including sub-directories) in that directory.


File: tar.info,  Node: extract,  Next: going further,  Prev: list,  Up: Tutorial

2.8 How to Extract Members from an Archive
==========================================

Creating an archive is only half the job—there is no point in storing
files in an archive if you can’t retrieve them.  The act of retrieving
members from an archive so they can be used and manipulated as
unarchived files again is called “extraction”.  To extract files from an
archive, use the ‘--extract’ (‘--get’ or ‘-x’) operation.  As with
‘--create’, specify the name of the archive with ‘--file’ (‘-f’) option.
Extracting an archive does not modify the archive in any way; you can
extract it multiple times if you want or need to.

   Using ‘--extract’, you can extract an entire archive, or specific
files.  The files can be directories containing other files, or not.  As
with ‘--create’ (‘-c’) and ‘--list’ (‘-t’), you may use the short or the
long form of the operation without affecting the performance.

* Menu:

* extracting archives::
* extracting files::
* extract dir::
* extracting untrusted archives::
* failing commands::


File: tar.info,  Node: extracting archives,  Next: extracting files,  Up: extract

2.8.1 Extracting an Entire Archive
----------------------------------

To extract an entire archive, specify the archive file name only, with
no individual file names as arguments.  For example,

     $ tar -xvf collection.tar

produces this:

     -rw-r--r-- myself/user      28 1996-10-18 16:31 jazz
     -rw-r--r-- myself/user      21 1996-09-23 16:44 blues
     -rw-r--r-- myself/user      20 1996-09-23 16:44 folk


File: tar.info,  Node: extracting files,  Next: extract dir,  Prev: extracting archives,  Up: extract

2.8.2 Extracting Specific Files
-------------------------------

To extract specific archive members, give their exact member names as
arguments, as printed by ‘--list’ (‘-t’).  If you had mistakenly deleted
one of the files you had placed in the archive ‘collection.tar’ earlier
(say, ‘blues’), you can extract it from the archive without changing the
archive’s structure.  Its contents will be identical to the original
file ‘blues’ that you deleted.

   First, make sure you are in the ‘practice’ directory, and list the
files in the directory.  Now, delete the file, ‘blues’, and list the
files in the directory again.

   You can now extract the member ‘blues’ from the archive file
‘collection.tar’ like this:

     $ tar --extract --file=collection.tar blues

If you list the files in the directory again, you will see that the file
‘blues’ has been restored, with its original permissions, data
modification times, and owner.(1)  (These parameters will be identical
to those which the file had when you originally placed it in the
archive; any changes you may have made before deleting the file from the
file system, however, will _not_ have been made to the archive member.)
The archive file, ‘collection.tar’, is the same as it was before you
extracted ‘blues’.  You can confirm this by running ‘tar’ with ‘--list’
(‘-t’).

   Remember that as with other operations, specifying the exact member
name is important (*Note failing commands::, for more examples).

   You can extract a file to standard output by combining the above
options with the ‘--to-stdout’ (‘-O’) option (*note Writing to Standard
Output::).

   If you give the ‘--verbose’ option, then ‘--extract’ will print the
names of the archive members as it extracts them.

   ---------- Footnotes ----------

   (1) This is only accidentally true, but not in general.  Whereas
modification times are always restored, in most cases, one has to be
root for restoring the owner, and use a special option for restoring
permissions.  Here, it just happens that the restoring user is also the
owner of the archived members, and that the current ‘umask’ is
compatible with original permissions.


File: tar.info,  Node: extract dir,  Next: extracting untrusted archives,  Prev: extracting files,  Up: extract

2.8.3 Extracting Files that are Directories
-------------------------------------------

Extracting directories which are members of an archive is similar to
extracting other files.  The main difference to be aware of is that if
the extracted directory has the same name as any directory already in
the working directory, then files in the extracted directory will be
placed into the directory of the same name.  Likewise, if there are
files in the pre-existing directory with the same names as the members
which you extract, the files from the extracted archive will replace the
files already in the working directory (and possible subdirectories).
This will happen regardless of whether or not the files in the working
directory were more recent than those extracted (there exist, however,
special options that alter this behavior *note Writing::).

   However, if a file was stored with a directory name as part of its
file name, and that directory does not exist under the working directory
when the file is extracted, ‘tar’ will create the directory.

   We can demonstrate how to use ‘--extract’ to extract a directory file
with an example.  Change to the ‘practice’ directory if you weren’t
there, and remove the files ‘folk’ and ‘jazz’.  Then, go back to the
parent directory and extract the archive ‘music.tar’.  You may either
extract the entire archive, or you may extract only the files you just
deleted.  To extract the entire archive, don’t give any file names as
arguments after the archive name ‘music.tar’.  To extract only the files
you deleted, use the following command:

     $ tar -xvf music.tar practice/folk practice/jazz
     practice/folk
     practice/jazz

If you were to specify two ‘--verbose’ (‘-v’) options, ‘tar’ would have
displayed more detail about the extracted files, as shown in the example
below:

     $ tar -xvvf music.tar practice/folk practice/jazz
     -rw-r--r-- me/user          28 1996-10-18 16:31 practice/jazz
     -rw-r--r-- me/user          20 1996-09-23 16:44 practice/folk

Because you created the directory with ‘practice’ as part of the file
names of each of the files by archiving the ‘practice’ directory as
‘practice’, you must give ‘practice’ as part of the file names when you
extract those files from the archive.


File: tar.info,  Node: extracting untrusted archives,  Next: failing commands,  Prev: extract dir,  Up: extract

2.8.4 Extracting Archives from Untrusted Sources
------------------------------------------------

Extracting files from archives can overwrite files that already exist.
If you receive an archive from an untrusted source, you should make a
new directory and extract into that directory, so that you don’t have to
worry about the extraction overwriting one of your existing files.  For
example, if ‘untrusted.tar’ came from somewhere else on the Internet,
and you don’t necessarily trust its contents, you can extract it as
follows:

     $ mkdir newdir
     $ cd newdir
     $ tar -xvf ../untrusted.tar

   It is also a good practice to examine contents of the archive before
extracting it, using ‘--list’ (‘-t’) option, possibly combined with
‘--verbose’ (‘-v’).


File: tar.info,  Node: failing commands,  Prev: extracting untrusted archives,  Up: extract

2.8.5 Commands That Will Fail
-----------------------------

Here are some sample commands you might try which will not work, and why
they won’t work.

   If you try to use this command,

     $ tar -xvf music.tar folk jazz

you will get the following response:

     tar: folk: Not found in archive
     tar: jazz: Not found in archive

This is because these files were not originally _in_ the parent
directory ‘..’, where the archive is located; they were in the
‘practice’ directory, and their file names reflect this:

     $ tar -tvf music.tar
     practice/blues
     practice/folk
     practice/jazz

Likewise, if you try to use this command,

     $ tar -tvf music.tar folk jazz

you would get a similar response.  Members with those names are not in
the archive.  You must use the correct member names, or wildcards, in
order to extract the files from the archive.

   If you have forgotten the correct names of the files in the archive,
use ‘tar --list --verbose’ to list them correctly.

   To extract the member named ‘practice/folk’, you must specify

     $ tar --extract --file=music.tar practice/folk

Notice also, that as explained above, the ‘practice’ directory will be
created, if it didn’t already exist.  There are options that allow you
to strip away a certain number of leading directory components (*note
transform::).  For example,

     $ tar --extract --file=music.tar --strip-components=1 folk

will extract the file ‘folk’ into the current working directory.


File: tar.info,  Node: going further,  Prev: extract,  Up: Tutorial

2.9 Going Further Ahead in this Manual
======================================

     _(This message will disappear, once this node revised.)_


File: tar.info,  Node: tar invocation,  Next: operations,  Prev: Tutorial,  Up: Top

3 Invoking GNU ‘tar’
********************

This chapter is about how one invokes the GNU ‘tar’ command, from the
command synopsis (*note Synopsis::).  There are numerous options, and
many styles for writing them.  One mandatory option specifies the
operation ‘tar’ should perform (*note Operation Summary::), other
options are meant to detail how this operation should be performed
(*note Option Summary::).  Non-option arguments are not always
interpreted the same way, depending on what the operation is.

   You will find in this chapter everything about option styles and
rules for writing them (*note Styles::).  On the other hand, operations
and options are fully described elsewhere, in other chapters.  Here, you
will find only synthetic descriptions for operations and options,
together with pointers to other parts of the ‘tar’ manual.

   Some options are so special they are fully described right in this
chapter.  They have the effect of inhibiting the normal operation of
‘tar’ or else, they globally alter the amount of feedback the user
receives about what is going on.  These are the ‘--help’ and ‘--version’
(*note help::), ‘--verbose’ (*note verbose::) and ‘--interactive’
options (*note interactive::).

* Menu:

* Synopsis::
* using tar options::
* Styles::
* All Options::           All ‘tar’ Options.
* help::                  Where to Get Help.
* defaults::              What are the Default Values.
* verbose::               Checking ‘tar’ progress.
* checkpoints::           Checkpoints.
* warnings::              Controlling Warning Messages.
* interactive::           Asking for Confirmation During Operations.
* external::              Running External Commands.


File: tar.info,  Node: Synopsis,  Next: using tar options,  Up: tar invocation

3.1 General Synopsis of ‘tar’
=============================

The GNU ‘tar’ program is invoked as either one of:

     tar OPTION... [NAME]...
     tar LETTER... [ARGUMENT]... [OPTION]... [NAME]...

   The second form is for when old options are being used.

   You can use ‘tar’ to store files in an archive, to extract them from
an archive, and to do other types of archive manipulation.  The primary
argument to ‘tar’, which is called the “operation”, specifies which
action to take.  The other arguments to ‘tar’ are either “options”,
which change the way ‘tar’ performs an operation, or file names or
archive members, which specify the files or members ‘tar’ is to act on.

   You can actually type in arguments in any order, even if in this
manual the options always precede the other arguments, to make examples
easier to understand.  Further, the option stating the main operation
mode (the ‘tar’ main command) is usually given first.

   Each NAME in the synopsis above is interpreted as an archive member
name when the main command is one of ‘--compare’ (‘--diff’, ‘-d’),
‘--delete’, ‘--extract’ (‘--get’, ‘-x’), ‘--list’ (‘-t’) or ‘--update’
(‘-u’).  When naming archive members, you must give the exact name of
the member in the archive, as it is printed by ‘--list’.  For ‘--append’
(‘-r’) and ‘--create’ (‘-c’), these NAME arguments specify the names of
either files or directory hierarchies to place in the archive.  These
files or hierarchies should already exist in the file system, prior to
the execution of the ‘tar’ command.

   ‘tar’ interprets relative file names as being relative to the working
directory.  ‘tar’ will make all file names relative (by removing leading
slashes when archiving or restoring files), unless you specify otherwise
(using the ‘--absolute-names’ option).  *Note absolute::, for more
information about ‘--absolute-names’.

   If you give the name of a directory as either a file name or a member
name, then ‘tar’ acts recursively on all the files and directories
beneath that directory.  For example, the name ‘/’ identifies all the
files in the file system to ‘tar’.

   The distinction between file names and archive member names is
especially important when shell globbing is used, and sometimes a source
of confusion for newcomers.  *Note wildcards::, for more information
about globbing.  The problem is that shells may only glob using existing
files in the file system.  Only ‘tar’ itself may glob on archive
members, so when needed, you must ensure that wildcard characters reach
‘tar’ without being interpreted by the shell first.  Using a backslash
before ‘*’ or ‘?’, or putting the whole argument between quotes, is
usually sufficient for this.

   Even if NAMEs are often specified on the command line, they can also
be read from a text file in the file system, using the
‘--files-from=FILE-OF-NAMES’ (‘-T FILE-OF-NAMES’) option.

   If you don’t use any file name arguments, ‘--append’ (‘-r’),
‘--delete’ and ‘--concatenate’ (‘--catenate’, ‘-A’) will do nothing,
while ‘--create’ (‘-c’) will usually yield a diagnostic and inhibit
‘tar’ execution.  The other operations of ‘tar’ (‘--list’, ‘--extract’,
‘--compare’, and ‘--update’) will act on the entire contents of the
archive.

   Besides successful exits, GNU ‘tar’ may fail for many reasons.  Some
reasons correspond to bad usage, that is, when the ‘tar’ command line is
improperly written.  Errors may be encountered later, while processing
the archive or the files.  Some errors are recoverable, in which case
the failure is delayed until ‘tar’ has completed all its work.  Some
errors are such that it would be not meaningful, or at least risky, to
continue processing: ‘tar’ then aborts processing immediately.  All
abnormal exits, whether immediate or delayed, should always be clearly
diagnosed on ‘stderr’, after a line stating the nature of the error.

   Possible exit codes of GNU ‘tar’ are summarized in the following
table:

0
     ‘Successful termination’.

1
     ‘Some files differ’.  If tar was invoked with ‘--compare’
     (‘--diff’, ‘-d’) command line option, this means that some files in
     the archive differ from their disk counterparts (*note compare::).
     If tar was given ‘--create’, ‘--append’ or ‘--update’ option, this
     exit code means that some files were changed while being archived
     and so the resulting archive does not contain the exact copy of the
     file set.

2
     ‘Fatal error’.  This means that some fatal, unrecoverable error
     occurred.

   If ‘tar’ has invoked a subprocess and that subprocess exited with a
nonzero exit code, ‘tar’ exits with that code as well.  This can happen,
for example, if ‘tar’ was given some compression option (*note gzip::)
and the external compressor program failed.  Another example is ‘rmt’
failure during backup to the remote device (*note Remote Tape Server::).


File: tar.info,  Node: using tar options,  Next: Styles,  Prev: Synopsis,  Up: tar invocation

3.2 Using ‘tar’ Options
=======================

GNU ‘tar’ has a total of eight operating modes which allow you to
perform a variety of tasks.  You are required to choose one operating
mode each time you employ the ‘tar’ program by specifying one, and only
one operation as an argument to the ‘tar’ command (the corresponding
options may be found at *note frequent operations:: and *note
Operations::).  Depending on circumstances, you may also wish to
customize how the chosen operating mode behaves.  For example, you may
wish to change the way the output looks, or the format of the files that
you wish to archive may require you to do something special in order to
make the archive look right.

   You can customize and control ‘tar’’s performance by running ‘tar’
with one or more options (such as ‘--verbose’ (‘-v’), which we used in
the tutorial).  As we said in the tutorial, “options” are arguments to
‘tar’ which are (as their name suggests) optional.  Depending on the
operating mode, you may specify one or more options.  Different options
will have different effects, but in general they all change details of
the operation, such as archive format, archive name, or level of user
interaction.  Some options make sense with all operating modes, while
others are meaningful only with particular modes.  You will likely use
some options frequently, while you will only use others infrequently, or
not at all.  (A full list of options is available in *note All
Options::.)

   The ‘TAR_OPTIONS’ environment variable specifies default options to
be placed in front of any explicit options.  For example, if
‘TAR_OPTIONS’ is ‘-v --unlink-first’, ‘tar’ behaves as if the two
options ‘-v’ and ‘--unlink-first’ had been specified before any explicit
options.  Option specifications are separated by whitespace.  A
backslash escapes the next character, so it can be used to specify an
option containing whitespace or a backslash.

   Note that ‘tar’ options are case sensitive.  For example, the options
‘-T’ and ‘-t’ are different; the first requires an argument for stating
the name of a file providing a list of NAMEs, while the second does not
require an argument and is another way to write ‘--list’ (‘-t’).

   In addition to the eight operations, there are many options to ‘tar’,
and three different styles for writing both: long (mnemonic) form, short
form, and old style.  These styles are discussed below.  Both the
options and the operations can be written in any of these three styles.


File: tar.info,  Node: Styles,  Next: All Options,  Prev: using tar options,  Up: tar invocation

3.3 The Three Option Styles
===========================

There are three styles for writing operations and options to the command
line invoking ‘tar’.  The different styles were developed at different
times during the history of ‘tar’.  These styles will be presented
below, from the most recent to the oldest.

   Some options must take an argument(1).  Where you _place_ the
arguments generally depends on which style of options you choose.  We
will detail specific information relevant to each option style in the
sections on the different option styles, below.  The differences are
subtle, yet can often be very important; incorrect option placement can
cause you to overwrite a number of important files.  We urge you to note
these differences, and only use the option style(s) which makes the most
sense to you until you feel comfortable with the others.

   Some options _may_ take an argument.  Such options may have at most
long and short forms, they do not have old style equivalent.  The rules
for specifying an argument for such options are stricter than those for
specifying mandatory arguments.  Please, pay special attention to them.

* Menu:

* Long Options::                Long Option Style
* Short Options::               Short Option Style
* Old Options::                 Old Option Style
* Mixing::                      Mixing Option Styles

   ---------- Footnotes ----------

   (1) For example, ‘--file’ (‘-f’) takes the name of an archive file as
an argument.  If you do not supply an archive file name, ‘tar’ will use
a default, but this can be confusing; thus, we recommend that you always
supply a specific archive file name.


File: tar.info,  Node: Long Options,  Next: Short Options,  Up: Styles

3.3.1 Long Option Style
-----------------------

Each option has at least one “long” (or “mnemonic”) name starting with
two dashes in a row, e.g., ‘--list’.  The long names are more clear than
their corresponding short or old names.  It sometimes happens that a
single long option has many different names which are synonymous, such
as ‘--compare’ and ‘--diff’.  In addition, long option names can be
given unique abbreviations.  For example, ‘--cre’ can be used in place
of ‘--create’ because there is no other long option which begins with
‘cre’.  (One way to find this out is by trying it and seeing what
happens; if a particular abbreviation could represent more than one
option, ‘tar’ will tell you that that abbreviation is ambiguous and
you’ll know that that abbreviation won’t work.  You may also choose to
run ‘tar --help’ to see a list of options.  Be aware that if you run
‘tar’ with a unique abbreviation for the long name of an option you
didn’t want to use, you are stuck; ‘tar’ will perform the command as
ordered.)

   Long options are meant to be obvious and easy to remember, and their
meanings are generally easier to discern than those of their
corresponding short options (see below).  For example:

     $ tar --create --verbose --blocking-factor=20 --file=/dev/rmt0

gives a fairly good set of hints about what the command does, even for
those not fully acquainted with ‘tar’.

   Long options which require arguments take those arguments immediately
following the option name.  There are two ways of specifying a mandatory
argument.  It can be separated from the option name either by an equal
sign, or by any amount of white space characters.  For example, the
‘--file’ option (which tells the name of the ‘tar’ archive) is given a
file such as ‘archive.tar’ as argument by using any of the following
notations: ‘--file=archive.tar’ or ‘--file archive.tar’.

   In contrast, optional arguments must always be introduced using an
equal sign.  For example, the ‘--backup’ option takes an optional
argument specifying backup type.  It must be used as
‘--backup=BACKUP-TYPE’.


File: tar.info,  Node: Short Options,  Next: Old Options,  Prev: Long Options,  Up: Styles

3.3.2 Short Option Style
------------------------

Most options also have a “short option” name.  Short options start with
a single dash, and are followed by a single character, e.g., ‘-t’ (which
is equivalent to ‘--list’).  The forms are absolutely identical in
function; they are interchangeable.

   The short option names are faster to type than long option names.

   Short options which require arguments take their arguments
immediately following the option, usually separated by white space.  It
is also possible to stick the argument right after the short option
name, using no intervening space.  For example, you might write
‘-f archive.tar’ or ‘-farchive.tar’ instead of using
‘--file=archive.tar’.  Both ‘--file=ARCHIVE-NAME’ and ‘-f ARCHIVE-NAME’
denote the option which indicates a specific archive, here named
‘archive.tar’.

   Short options which take optional arguments take their arguments
immediately following the option letter, _without any intervening white
space characters_.

   Short options’ letters may be clumped together, but you are not
required to do this (as compared to old options; see below).  When short
options are clumped as a set, use one (single) dash for them all, e.g.,
‘‘tar’ -cvf’.  Only the last option in such a set is allowed to have an
argument(1).

   When the options are separated, the argument for each option which
requires an argument directly follows that option, as is usual for Unix
programs.  For example:

     $ tar -c -v -b 20 -f /dev/rmt0

   If you reorder short options’ locations, be sure to move any
arguments that belong to them.  If you do not move the arguments
properly, you may end up overwriting files.

   ---------- Footnotes ----------

   (1) Clustering many options, the last of which has an argument, is a
rather opaque way to write options.  Some wonder if GNU ‘getopt’ should
not even be made helpful enough for considering such usages as invalid.


File: tar.info,  Node: Old Options,  Next: Mixing,  Prev: Short Options,  Up: Styles

3.3.3 Old Option Style
----------------------

As far as we know, all ‘tar’ programs, GNU and non-GNU, support “old
options”: that is, if the first argument does not start with ‘-’, it is
assumed to specify option letters.  GNU ‘tar’ supports old options not
only for historical reasons, but also because many people are used to
them.  If the first argument does not start with a dash, you are
announcing the old option style instead of the short option style; old
options are decoded differently.

   Like short options, old options are single letters.  However, old
options must be written together as a single clumped set, without spaces
separating them or dashes preceding them.  This set of letters must be
the first to appear on the command line, after the ‘tar’ program name
and some white space; old options cannot appear anywhere else.  The
letter of an old option is exactly the same letter as the corresponding
short option.  For example, the old option ‘t’ is the same as the short
option ‘-t’, and consequently, the same as the long option ‘--list’.  So
for example, the command ‘tar cv’ specifies the option ‘-v’ in addition
to the operation ‘-c’.

   When options that need arguments are given together with the command,
all the associated arguments follow, in the same order as the options.
Thus, the example given previously could also be written in the old
style as follows:

     $ tar cvbf 20 /dev/rmt0

Here, ‘20’ is the argument of ‘-b’ and ‘/dev/rmt0’ is the argument of
‘-f’.

   The old style syntax can make it difficult to match option letters
with their corresponding arguments, and is often confusing.  In the
command ‘tar cvbf 20 /dev/rmt0’, for example, ‘20’ is the argument for
‘-b’, ‘/dev/rmt0’ is the argument for ‘-f’, and ‘-v’ does not have a
corresponding argument.  Even using short options like in
‘tar -c -v -b 20 -f /dev/rmt0’ is clearer, putting all arguments next to
the option they pertain to.

   If you want to reorder the letters in the old option argument, be
sure to reorder any corresponding argument appropriately.

   This old way of writing ‘tar’ options can surprise even experienced
users.  For example, the two commands:

     tar cfz archive.tar.gz file
     tar -cfz archive.tar.gz file

are quite different.  The first example uses ‘archive.tar.gz’ as the
value for option ‘f’ and recognizes the option ‘z’.  The second example,
however, uses ‘z’ as the value for option ‘f’ — probably not what was
intended.

   This second example could be corrected in many ways, among which the
following are equivalent:

     tar -czf archive.tar.gz file
     tar -cf archive.tar.gz -z file
     tar cf archive.tar.gz -z file


File: tar.info,  Node: Mixing,  Prev: Old Options,  Up: Styles

3.3.4 Mixing Option Styles
--------------------------

All three styles may be intermixed in a single ‘tar’ command, so long as
the rules for each style are fully respected(1).  Old style options and
either of the modern styles of options may be mixed within a single
‘tar’ command.  However, old style options must be introduced as the
first arguments only, following the rule for old options (old options
must appear directly after the ‘tar’ command and some white space).
Modern options may be given only after all arguments to the old options
have been collected.  If this rule is not respected, a modern option
might be falsely interpreted as the value of the argument to one of the
old style options.

   For example, all the following commands are wholly equivalent, and
illustrate the many combinations and orderings of option styles.

     tar --create --file=archive.tar
     tar --create -f archive.tar
     tar --create -farchive.tar
     tar --file=archive.tar --create
     tar --file=archive.tar -c
     tar -c --file=archive.tar
     tar -c -f archive.tar
     tar -c -farchive.tar
     tar -cf archive.tar
     tar -cfarchive.tar
     tar -f archive.tar --create
     tar -f archive.tar -c
     tar -farchive.tar --create
     tar -farchive.tar -c
     tar c --file=archive.tar
     tar c -f archive.tar
     tar c -farchive.tar
     tar cf archive.tar
     tar f archive.tar --create
     tar f archive.tar -c
     tar fc archive.tar

   On the other hand, the following commands are _not_ equivalent to the
previous set:

     tar -f -c archive.tar
     tar -fc archive.tar
     tar -fcarchive.tar
     tar -farchive.tarc
     tar cfarchive.tar

These last examples mean something completely different from what the
user intended (judging based on the example in the previous set which
uses long options, whose intent is therefore very clear).  The first
four specify that the ‘tar’ archive would be a file named ‘-c’, ‘c’,
‘carchive.tar’ or ‘archive.tarc’, respectively.  The first two examples
also specify a single non-option, NAME argument having the value
‘archive.tar’.  The last example contains only old style option letters
(repeating option ‘c’ twice), not all of which are meaningful (eg., ‘.’,
‘h’, or ‘i’), with no argument value.

   ---------- Footnotes ----------

   (1) Before GNU ‘tar’ version 1.11.6, a bug prevented intermixing old
style options with long options in some cases.


File: tar.info,  Node: All Options,  Next: help,  Prev: Styles,  Up: tar invocation

3.4 All ‘tar’ Options
=====================

The coming manual sections contain an alphabetical listing of all ‘tar’
operations and options, with brief descriptions and cross-references to
more in-depth explanations in the body of the manual.  They also contain
an alphabetically arranged table of the short option forms with their
corresponding long option.  You can use this table as a reference for
deciphering ‘tar’ commands in scripts.

* Menu:

* Operation Summary::
* Option Summary::
* Short Option Summary::
* Position-Sensitive Options::


File: tar.info,  Node: Operation Summary,  Next: Option Summary,  Up: All Options

3.4.1 Operations
----------------

‘--append’
‘-r’

     Appends files to the end of the archive.  *Note append::.

‘--catenate’
‘-A’

     Same as ‘--concatenate’.  *Note concatenate::.

‘--compare’
‘-d’

     Compares archive members with their counterparts in the file
     system, and reports differences in file size, mode, owner,
     modification date and contents.  *Note compare::.

‘--concatenate’
‘-A’

     Appends other ‘tar’ archives to the end of the archive.  *Note
     concatenate::.

‘--create’
‘-c’

     Creates a new ‘tar’ archive.  *Note create::.

‘--delete’

     Deletes members from the archive.  Don’t try this on an archive on
     a tape!  *Note delete::.

‘--diff’
‘-d’

     Same as ‘--compare’.  *Note compare::.

‘--extract’
‘-x’

     Extracts members from the archive into the file system.  *Note
     extract::.

‘--get’
‘-x’

     Same as ‘--extract’.  *Note extract::.

‘--list’
‘-t’

     Lists the members in an archive.  *Note list::.

‘--update’
‘-u’

     Adds files to the end of the archive, but only if they are newer
     than their counterparts already in the archive, or if they do not
     already exist in the archive.  *Note update::.


File: tar.info,  Node: Option Summary,  Next: Short Option Summary,  Prev: Operation Summary,  Up: All Options

3.4.2 ‘tar’ Options
-------------------

‘--absolute-names’
‘-P’

     Normally when creating an archive, ‘tar’ strips an initial ‘/’ from
     member names, and when extracting from an archive ‘tar’ treats
     names specially if they have initial ‘/’ or internal ‘..’.  This
     option disables that behavior.  *Note absolute::.

‘--acls’
     Enable POSIX ACLs support.  *Note acls: Extended File Attributes.

‘--after-date’

     (See ‘--newer’, *note after::)

‘--anchored’
     A pattern must match an initial subsequence of the name’s
     components.  *Note controlling pattern-matching::.

‘--atime-preserve’
‘--atime-preserve=replace’
‘--atime-preserve=system’

     Attempt to preserve the access time of files when reading them.
     This option currently is effective only on files that you own,
     unless you have superuser privileges.

     ‘--atime-preserve=replace’ remembers the access time of a file
     before reading it, and then restores the access time afterwards.
     This may cause problems if other programs are reading the file at
     the same time, as the times of their accesses will be lost.  On
     most platforms restoring the access time also requires ‘tar’ to
     restore the data modification time too, so this option may also
     cause problems if other programs are writing the file at the same
     time (‘tar’ attempts to detect this situation, but cannot do so
     reliably due to race conditions).  Worse, on most platforms
     restoring the access time also updates the status change time,
     which means that this option is incompatible with incremental
     backups.

     ‘--atime-preserve=system’ avoids changing time stamps on files,
     without interfering with time stamp updates caused by other
     programs, so it works better with incremental backups.  However, it
     requires a special ‘O_NOATIME’ option from the underlying operating
     and file system implementation, and it also requires that searching
     directories does not update their access times.  As of this writing
     (November 2005) this works only with Linux, and only with Linux
     kernels 2.6.8 and later.  Worse, there is currently no reliable way
     to know whether this feature actually works.  Sometimes ‘tar’ knows
     that it does not work, and if you use ‘--atime-preserve=system’
     then ‘tar’ complains and exits right away.  But other times ‘tar’
     might think that the option works when it actually does not.

     Currently ‘--atime-preserve’ with no operand defaults to
     ‘--atime-preserve=replace’, but this may change in the future as
     support for ‘--atime-preserve=system’ improves.

     If your operating or file system does not support
     ‘--atime-preserve=system’, you might be able to preserve access
     times reliably by using the ‘mount’ command.  For example, you can
     mount the file system read-only, or access the file system via a
     read-only loopback mount, or use the ‘noatime’ mount option
     available on some systems.  However, mounting typically requires
     superuser privileges and can be a pain to manage.

‘--auto-compress’
‘-a’

     During a ‘--create’ operation, enables automatic compressed format
     recognition based on the archive suffix.  The effect of this option
     is cancelled by ‘--no-auto-compress’.  *Note gzip::.

‘--backup=BACKUP-TYPE’

     Rather than deleting files from the file system, ‘tar’ will back
     them up using simple or numbered backups, depending upon
     BACKUP-TYPE.  *Note backup::.

‘--block-number’
‘-R’

     With this option present, ‘tar’ prints error messages for read
     errors with the block number in the archive file.  *Note
     block-number::.

‘--blocking-factor=BLOCKING’
‘-b BLOCKING’

     Sets the blocking factor ‘tar’ uses to BLOCKING x 512 bytes per
     record.  *Note Blocking Factor::.

‘--bzip2’
‘-j’

     This option tells ‘tar’ to read or write archives through ‘bzip2’.
     *Note gzip::.

‘--check-device’
     Check device numbers when creating a list of modified files for
     incremental archiving.  This is the default.  *Note device
     numbers::, for a detailed description.

‘--checkpoint[=NUMBER]’

     This option directs ‘tar’ to print periodic checkpoint messages as
     it reads through the archive.  It is intended for when you want a
     visual indication that ‘tar’ is still running, but don’t want to
     see ‘--verbose’ output.  You can also instruct ‘tar’ to execute a
     list of actions on each checkpoint, see ‘--checkpoint-action’
     below.  For a detailed description, see *note checkpoints::.

‘--checkpoint-action=ACTION’
     Instruct ‘tar’ to execute an action upon hitting a breakpoint.
     Here we give only a brief outline.  *Note checkpoints::, for a
     complete description.

     The ACTION argument can be one of the following:

     bell
          Produce an audible bell on the console.

     dot
     .
          Print a single dot on the standard listing stream.

     echo
          Display a textual message on the standard error, with the
          status and number of the checkpoint.  This is the default.

     echo=STRING
          Display STRING on the standard error.  Before output, the
          string is subject to meta-character expansion.

     exec=COMMAND
          Execute the given COMMAND.

     sleep=TIME
          Wait for TIME seconds.

     ttyout=STRING
          Output STRING on the current console (‘/dev/tty’).

     totals
          Print statistics (see *note totals::).

     wait=SIGNO
          Wait for signal SIGNO.

     Several ‘--checkpoint-action’ options can be specified.  The
     supplied actions will be executed in order of their appearance in
     the command line.

     Using ‘--checkpoint-action’ without ‘--checkpoint’ assumes default
     checkpoint frequency of one checkpoint per 10 records.

‘--check-links’
‘-l’
     If this option was given, ‘tar’ will check the number of links
     dumped for each processed file.  If this number does not match the
     total number of hard links for the file, a warning message will be
     output (1).

     *Note hard links::.

‘--compress’
‘--uncompress’
‘-Z’

     ‘tar’ will use the ‘compress’ program when reading or writing the
     archive.  This allows you to directly act on archives while saving
     space.  *Note gzip::.

‘--clamp-mtime’

     (See ‘--mtime’.)

‘--confirmation’

     (See ‘--interactive’.)  *Note interactive::.

‘--delay-directory-restore’

     Delay setting modification times and permissions of extracted
     directories until the end of extraction.  *Note Directory
     Modification Times and Permissions::.

‘--dereference’
‘-h’

     When reading or writing a file to be archived, ‘tar’ accesses the
     file that a symbolic link points to, rather than the symlink
     itself.  *Note dereference::.

‘--directory=DIR’
‘-C DIR’

     When this option is specified, ‘tar’ will change its current
     directory to DIR before performing any operations.  When this
     option is used during archive creation, it is order sensitive.
     *Note directory::.

‘--exclude=PATTERN’

     When performing operations, ‘tar’ will skip files that match
     PATTERN.  *Note exclude::.

‘--exclude-backups’
     Exclude backup and lock files.  *Note exclude-backups: exclude.

‘--exclude-from=FILE’
‘-X FILE’

     Similar to ‘--exclude’, except ‘tar’ will use the list of patterns
     in the file FILE.  *Note exclude::.

‘--exclude-caches’

     Exclude from dump any directory containing a valid cache directory
     tag file, but still dump the directory node and the tag file
     itself.

     *Note exclude-caches: exclude.

‘--exclude-caches-under’

     Exclude from dump any directory containing a valid cache directory
     tag file, but still dump the directory node itself.

     *Note exclude::.

‘--exclude-caches-all’

     Exclude from dump any directory containing a valid cache directory
     tag file.  *Note exclude::.

‘--exclude-ignore=FILE’
     Before dumping a directory, ‘tar’ checks if it contains FILE.  If
     so, exclusion patterns are read from this file.  The patterns
     affect only the directory itself.  *Note exclude::.

‘--exclude-ignore-recursive=FILE’
     Before dumping a directory, ‘tar’ checks if it contains FILE.  If
     so, exclusion patterns are read from this file.  The patterns
     affect the directory and all itssubdirectories.  *Note exclude::.

‘--exclude-tag=FILE’

     Exclude from dump any directory containing file named FILE, but
     dump the directory node and FILE itself.  *Note exclude-tag:
     exclude.

‘--exclude-tag-under=FILE’

     Exclude from dump the contents of any directory containing file
     named FILE, but dump the directory node itself.  *Note
     exclude-tag-under: exclude.

‘--exclude-tag-all=FILE’

     Exclude from dump any directory containing file named FILE.  *Note
     exclude-tag-all: exclude.

‘--exclude-vcs’

     Exclude from dump directories and files, that are internal for some
     widely used version control systems.

     *Note exclude-vcs::.

‘--exclude-vcs-ignores’
     Exclude files that match patterns read from VCS-specific ignore
     files.  Supported files are: ‘.cvsignore’, ‘.gitignore’,
     ‘.bzrignore’, and ‘.hgignore’.  The semantics of each file is the
     same as for the corresponding VCS, e.g.  patterns read from
     ‘.gitignore’ affect the directory and all its subdirectories.
     *Note exclude-vcs-ignores::.

‘--file=ARCHIVE’
‘-f ARCHIVE’

     ‘tar’ will use the file ARCHIVE as the ‘tar’ archive it performs
     operations on, rather than ‘tar’’s compilation dependent default.
     *Note file tutorial::.

‘--files-from=FILE’
‘-T FILE’

     ‘tar’ will use the contents of FILE as a list of archive members or
     files to operate on, in addition to those specified on the
     command-line.  *Note files::.

‘--force-local’

     Forces ‘tar’ to interpret the file name given to ‘--file’ as a
     local file, even if it looks like a remote tape drive name.  *Note
     local and remote archives::.

‘--format=FORMAT’
‘-H FORMAT’

     Selects output archive format.  FORMAT may be one of the following:

     ‘v7’
          Creates an archive that is compatible with Unix V7 ‘tar’.

     ‘oldgnu’
          Creates an archive that is compatible with GNU ‘tar’ version
          1.12 or earlier.

     ‘gnu’
          Creates archive in GNU tar 1.13 format.  Basically it is the
          same as ‘oldgnu’ with the only difference in the way it
          handles long numeric fields.

     ‘ustar’
          Creates a POSIX.1-1988 compatible archive.

     ‘posix’
          Creates a POSIX.1-2001 archive.

     *Note Formats::, for a detailed discussion of these formats.

‘--full-time’
     This option instructs ‘tar’ to print file times to their full
     resolution.  Usually this means 1-second resolution, but that
     depends on the underlying file system.  The ‘--full-time’ option
     takes effect only when detailed output (verbosity level 2 or
     higher) has been requested using the ‘--verbose’ option, e.g., when
     listing or extracting archives:

          $ tar -t -v --full-time -f archive.tar

     or, when creating an archive:

          $ tar -c -vv --full-time -f archive.tar .

     Notice, thar when creating the archive you need to specify
     ‘--verbose’ twice to get a detailed output (*note verbose
     tutorial::).

‘--group=GROUP’

     Files added to the ‘tar’ archive will have a group ID of GROUP,
     rather than the group from the source file.  GROUP can specify a
     symbolic name, or a numeric ID, or both as NAME:ID.  *Note
     override::.

     Also see the ‘--group-map’ option and comments for the
     ‘--owner=USER’ option.

‘--group-map=FILE’

     Read owner group translation map from FILE.  This option allows to
     translate only certain group names and/or UIDs.  *Note override::,
     for a detailed description.  When used together with ‘--group’
     option, the latter affects only those files whose owner group is
     not listed in the FILE.

     This option does not affect extraction from archives.

‘--gzip’
‘--gunzip’
‘--ungzip’
‘-z’

     This option tells ‘tar’ to read or write archives through ‘gzip’,
     allowing ‘tar’ to directly operate on several kinds of compressed
     archives transparently.  *Note gzip::.

‘--hard-dereference’
     When creating an archive, dereference hard links and store the
     files they refer to, instead of creating usual hard link members.

     *Note hard links::.

‘--help’
‘-?’

     ‘tar’ will print out a short message summarizing the operations and
     options to ‘tar’ and exit.  *Note help::.

‘--hole-detection=METHOD’
     Use METHOD to detect holes in sparse files.  This option implies
     ‘--sparse’.  Valid methods are ‘seek’ and ‘raw’.  Default is ‘seek’
     with fallback to ‘raw’ when not applicable.  *Note sparse::.

‘--ignore-case’
     Ignore case when matching member or file names with patterns.
     *Note controlling pattern-matching::.

‘--ignore-command-error’
     Ignore exit codes of subprocesses.  *Note Writing to an External
     Program::.

‘--ignore-failed-read’

     Do not exit unsuccessfully merely because reading failed.  *Note
     Ignore Failed Read::.

‘--ignore-zeros’
‘-i’

     With this option, ‘tar’ will ignore zeroed blocks in the archive,
     which normally signals EOF. This option also suppresses warnings
     about missing or incomplete zero blocks at the end of the archive.
     *Note Ignore Zeros::.

‘--incremental’
‘-G’

     Informs ‘tar’ that it is working with an old GNU-format incremental
     backup archive.  It is intended primarily for backwards
     compatibility only.  *Note Incremental Dumps::, for a detailed
     discussion of incremental archives.

‘--index-file=FILE’

     Send verbose output to FILE instead of to standard output.

‘--info-script=COMMAND’
‘--new-volume-script=COMMAND’
‘-F COMMAND’

     When ‘tar’ is performing multi-tape backups, COMMAND is run at the
     end of each tape.  If it exits with nonzero status, ‘tar’ fails
     immediately.  *Note info-script::, for a detailed discussion of
     this feature.

‘--interactive’
‘--confirmation’
‘-w’

     Specifies that ‘tar’ should ask the user for confirmation before
     performing potentially destructive options, such as overwriting
     files.  *Note interactive::.

‘--keep-directory-symlink’

     This option changes the behavior of tar when it encounters a
     symlink with the same name as the directory that it is about to
     extract.  By default, in this case tar would first remove the
     symlink and then proceed extracting the directory.

     The ‘--keep-directory-symlink’ option disables this behavior and
     instructs tar to follow symlinks to directories when extracting
     from the archive.

     It is mainly intended to provide compatibility with the Slackware
     installation scripts.

‘--keep-newer-files’

     Do not replace existing files that are newer than their archive
     copies when extracting files from an archive.

‘--keep-old-files’
‘-k’

     Do not overwrite existing files when extracting files from an
     archive.  Return error if such files exist.  See also *note
     --skip-old-files::.

     *Note Keep Old Files::.

‘--label=NAME’
‘-V NAME’

     When creating an archive, instructs ‘tar’ to write NAME as a name
     record in the archive.  When extracting or listing archives, ‘tar’
     will only operate on archives that have a label matching the
     pattern specified in NAME.  *Note Tape Files::.

‘--level=N’
     Force incremental backup of level N.  As of GNU ‘tar’ version 1.35,
     the option ‘--level=0’ truncates the snapshot file, thereby forcing
     the level 0 dump.  Other values of N are effectively ignored.
     *Note --level=0::, for details and examples.

     The use of this option is valid only in conjunction with the
     ‘--listed-incremental’ option.  *Note Incremental Dumps::, for a
     detailed description.

‘--listed-incremental=SNAPSHOT-FILE’
‘-g SNAPSHOT-FILE’

     During a ‘--create’ operation, specifies that the archive that
     ‘tar’ creates is a new GNU-format incremental backup, using
     SNAPSHOT-FILE to determine which files to backup.  With other
     operations, informs ‘tar’ that the archive is in incremental
     format.  *Note Incremental Dumps::.

‘--lzip’

     This option tells ‘tar’ to read or write archives through ‘lzip’.
     *Note gzip::.

‘--lzma’

     This option tells ‘tar’ to read or write archives through ‘lzma’.
     *Note gzip::.

‘--lzop’

     This option tells ‘tar’ to read or write archives through ‘lzop’.
     *Note gzip::.

‘--mode=PERMISSIONS’

     When adding files to an archive, ‘tar’ will use PERMISSIONS for the
     archive members, rather than the permissions from the files.
     PERMISSIONS can be specified either as an octal number or as
     symbolic permissions, like with ‘chmod’.  *Note override::.

‘--mtime=DATE’

     When adding files to an archive, ‘tar’ will use DATE as the
     modification time of members when creating archives, instead of
     their actual modification times.  The value of DATE can be either a
     textual date representation (*note Date input formats::) or a name
     of the existing file, starting with ‘/’ or ‘.’.  In the latter
     case, the modification time of that file is used.  *Note
     override::.

     When ‘--clamp-mtime’ is also specified, files with modification
     times earlier than DATE will retain their actual modification
     times, and DATE will only be used for files whose modification
     times are later than DATE.

‘--multi-volume’
‘-M’

     Informs ‘tar’ that it should create or otherwise operate on a
     multi-volume ‘tar’ archive.  *Note Using Multiple Tapes::.

‘--new-volume-script’

     (see ‘--info-script’)

‘--newer=DATE’
‘--after-date=DATE’
‘-N’

     When creating an archive, ‘tar’ will only add files that have
     changed since DATE.  If DATE begins with ‘/’ or ‘.’, it is taken to
     be the name of a file whose data modification time specifies the
     date.  *Note after::.

‘--newer-mtime=DATE’

     Like ‘--newer’, but add only files whose contents have changed (as
     opposed to just ‘--newer’, which will also back up files for which
     any status information has changed).  *Note after::.

‘--no-acls’
     Disable the POSIX ACLs support.  *Note acls: Extended File
     Attributes.

‘--no-anchored’
     An exclude pattern can match any subsequence of the name’s
     components.  *Note controlling pattern-matching::.

‘--no-auto-compress’

     Disables automatic compressed format recognition based on the
     archive suffix.  *Note --auto-compress::.  *Note gzip::.

‘--no-check-device’
     Do not check device numbers when creating a list of modified files
     for incremental archiving.  *Note device numbers::, for a detailed
     description.

‘--no-delay-directory-restore’

     Modification times and permissions of extracted directories are set
     when all files from this directory have been extracted.  This is
     the default.  *Note Directory Modification Times and Permissions::.

‘--no-ignore-case’
     Use case-sensitive matching.  *Note controlling pattern-matching::.

‘--no-ignore-command-error’
     Print warnings about subprocesses that terminated with a nonzero
     exit code.  *Note Writing to an External Program::.

‘--no-null’

     If the ‘--null’ option was given previously, this option cancels
     its effect, so that any following ‘--files-from’ options will
     expect their file lists to be newline-terminated.

‘--no-overwrite-dir’

     Preserve metadata of existing directories when extracting files
     from an archive.  *Note Overwrite Old Files::.

‘--no-quote-chars=STRING’
     Remove characters listed in STRING from the list of quoted
     characters set by the previous ‘--quote-chars’ option (*note
     quoting styles::).

‘--no-recursion’

     With this option, ‘tar’ will not recurse into directories.  *Note
     recurse::.

‘--no-same-owner’
‘-o’

     When extracting an archive, do not attempt to preserve the owner
     specified in the ‘tar’ archive.  This the default behavior for
     ordinary users.

‘--no-same-permissions’

     When extracting an archive, subtract the user’s umask from files
     from the permissions specified in the archive.  This is the default
     behavior for ordinary users.

‘--no-seek’

     The archive media does not support seeks to arbitrary locations.
     Usually ‘tar’ determines automatically whether the archive can be
     seeked or not.  Use this option to disable this mechanism.

‘--no-selinux’
     Disable SELinux context support.  *Note SELinux: Extended File
     Attributes.

‘--no-unquote’
     Treat all input file or member names literally, do not interpret
     escape sequences.  *Note input name quoting::.

‘--no-verbatim-files-from’

     Instructs GNU ‘tar’ to treat each line read from a file list as if
     it were supplied in the command line.  I.e., leading and trailing
     whitespace is removed and, if the result begins with a dash, it is
     treated as a GNU ‘tar’ command line option.

     This is default behavior.  This option is provided as a way to
     restore it after ‘--verbatim-files-from’ option.

     It is implied by the ‘--no-null’ option.

     *Note no-verbatim-files-from::.

‘--no-wildcards’
     Do not use wildcards.  *Note controlling pattern-matching::.

‘--no-wildcards-match-slash’
     Wildcards do not match ‘/’.  *Note controlling pattern-matching::.

‘--no-xattrs’
     Disable extended attributes support.  *Note xattrs: Extended File
     Attributes.

‘--null’

     When ‘tar’ is using the ‘--files-from’ option, this option
     instructs ‘tar’ to expect file names terminated with NUL, and to
     process file names verbatim.

     This means that ‘tar’ correctly works with file names that contain
     newlines or begin with a dash.

     *Note nul::.

     See also *note verbatim-files-from::.

‘--numeric-owner’

     This option will notify ‘tar’ that it should use numeric user and
     group IDs when creating a ‘tar’ file, rather than names.  *Note
     Attributes::.

‘-o’
     The function of this option depends on the action ‘tar’ is
     performing.  When extracting files, ‘-o’ is a synonym for
     ‘--no-same-owner’, i.e., it prevents ‘tar’ from restoring ownership
     of files being extracted.

     When creating an archive, it is a synonym for ‘--old-archive’.
     This behavior is for compatibility with previous versions of GNU
     ‘tar’, and will be removed in future releases.

     *Note Changes::, for more information.

‘--occurrence[=NUMBER]’

     This option can be used in conjunction with one of the subcommands
     ‘--delete’, ‘--diff’, ‘--extract’ or ‘--list’ when a list of files
     is given either on the command line or via ‘-T’ option.

     This option instructs ‘tar’ to process only the NUMBERth occurrence
     of each named file.  NUMBER defaults to 1, so

          tar -x -f archive.tar --occurrence filename

     will extract the first occurrence of the member ‘filename’ from
     ‘archive.tar’ and will terminate without scanning to the end of the
     archive.

‘--old-archive’
     Synonym for ‘--format=v7’.

‘--one-file-system’
     Used when creating an archive.  Prevents ‘tar’ from recursing into
     directories that are on different file systems from the current
     directory.

‘--one-top-level[=DIR]’
     Tells ‘tar’ to create a new directory beneath the extraction
     directory (or the one passed to ‘-C’) and use it to guard against
     tarbombs.  In the absence of DIR argument, the name of the new
     directory will be equal to the base name of the archive (file name
     minus the archive suffix, if recognized).  Any member names that do
     not begin with that directory name (after transformations from
     ‘--transform’ and ‘--strip-components’) will be prefixed with it.
     Recognized file name suffixes are ‘.tar’, and any compression
     suffixes recognizable by *Note --auto-compress::.

‘--overwrite’

     Overwrite existing files and directory metadata when extracting
     files from an archive.  *Note Overwrite Old Files::.

‘--overwrite-dir’

     Overwrite the metadata of existing directories when extracting
     files from an archive.  *Note Overwrite Old Files::.

‘--owner=USER’

     Specifies that ‘tar’ should use USER as the owner of members when
     creating archives, instead of the user associated with the source
     file.  USER can specify a symbolic name, or a numeric ID, or both
     as NAME:ID.  *Note override::.

     This option does not affect extraction from archives.  See also
     ‘--owner-map’, below.

‘--owner-map=FILE’

     Read owner translation map from FILE.  This option allows to
     translate only certain owner names or UIDs.  *Note override::, for
     a detailed description.  When used together with ‘--owner’ option,
     the latter affects only those files whose owner is not listed in
     the FILE.

     This option does not affect extraction from archives.

‘--pax-option=KEYWORD-LIST’
     This option enables creation of the archive in POSIX.1-2001 format
     (*note posix::) and modifies the way ‘tar’ handles the extended
     header keywords.  KEYWORD-LIST is a comma-separated list of keyword
     options.  *Note PAX keywords::, for a detailed discussion.

‘--portability’
‘--old-archive’
     Synonym for ‘--format=v7’.

‘--posix’
     Same as ‘--format=posix’.

‘--preserve-order’

     (See ‘--same-order’; *note Same Order::.)

‘--preserve-permissions’
‘--same-permissions’
‘-p’

     When ‘tar’ is extracting an archive, it normally subtracts the
     users’ umask from the permissions specified in the archive and uses
     that number as the permissions to create the destination file.
     Specifying this option instructs ‘tar’ that it should use the
     permissions directly from the archive.  *Note Setting Access
     Permissions::.

‘--quote-chars=STRING’
     Always quote characters from STRING, even if the selected quoting
     style would not quote them (*note quoting styles::).

‘--quoting-style=STYLE’
     Set quoting style to use when printing member and file names (*note
     quoting styles::).  Valid STYLE values are: ‘literal’, ‘shell’,
     ‘shell-always’, ‘c’, ‘escape’, ‘locale’, and ‘clocale’.  Default
     quoting style is ‘escape’, unless overridden while configuring the
     package.

‘--read-full-records’
‘-B’

     Specifies that ‘tar’ should reblock its input, for reading from
     pipes on systems with buggy implementations.  *Note Reading::.

‘--record-size=SIZE[SUF]’

     Instructs ‘tar’ to use SIZE bytes per record when accessing the
     archive.  The argument can be suffixed with a “size suffix”, e.g.
     ‘--record-size=10K’ for 10 Kilobytes.  *Note Table 9.1:
     size-suffixes, for a list of valid suffixes.  *Note Blocking
     Factor::, for a detailed description of this option.

‘--recursion’

     With this option, ‘tar’ recurses into directories (default).  *Note
     recurse::.

‘--recursive-unlink’

     Remove existing directory hierarchies before extracting directories
     of the same name from the archive.  *Note Recursive Unlink::.

‘--remove-files’

     Directs ‘tar’ to remove the source file from the file system after
     appending it to an archive.  *Note remove files::.

‘--restrict’

     Disable use of some potentially harmful ‘tar’ options.  Currently
     this option disables shell invocation from multi-volume menu (*note
     Using Multiple Tapes::).

‘--rmt-command=CMD’

     Notifies ‘tar’ that it should use CMD instead of the default
     ‘/usr/libexec/rmt’ (*note Remote Tape Server::).

‘--rsh-command=CMD’

     Notifies ‘tar’ that is should use CMD to communicate with remote
     devices.  *Note Device::.

‘--same-order’
‘--preserve-order’
‘-s’

     This option is an optimization for ‘tar’ when running on machines
     with small amounts of memory.  It informs ‘tar’ that the list of
     file arguments has already been sorted to match the order of files
     in the archive.  *Note Same Order::.

‘--same-owner’

     When extracting an archive, ‘tar’ will attempt to preserve the
     owner specified in the ‘tar’ archive with this option present.
     This is the default behavior for the superuser; this option has an
     effect only for ordinary users.  *Note Attributes::.

‘--same-permissions’

     (See ‘--preserve-permissions’; *note Setting Access Permissions::.)

‘--seek’
‘-n’

     Assume that the archive media supports seeks to arbitrary
     locations.  Usually ‘tar’ determines automatically whether the
     archive can be seeked or not.  This option is intended for use in
     cases when such recognition fails.  It takes effect only if the
     archive is open for reading (e.g.  with ‘--list’ or ‘--extract’
     options).

‘--selinux’
     Enable the SELinux context support.  *Note selinux: Extended File
     Attributes.

‘--show-defaults’

     Displays the default options used by ‘tar’ and exits successfully.
     This option is intended for use in shell scripts.  Here is an
     example of what you can see using this option:

          $ tar --show-defaults
          --format=gnu -f- -b20 --quoting-style=escape
          --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh

     Notice, that this option outputs only one line.  The example output
     above has been split to fit page boundaries.  *Note defaults::.

‘--show-omitted-dirs’

     Instructs ‘tar’ to mention the directories it is skipping when
     operating on a ‘tar’ archive.  *Note show-omitted-dirs::.

‘--show-snapshot-field-ranges’

     Displays the range of values allowed by this version of ‘tar’ for
     each field in the snapshot file, then exits successfully.  *Note
     Snapshot Files::.

‘--show-transformed-names’
‘--show-stored-names’

     Display file or member names after applying any transformations
     (*note transform::).  In particular, when used in conjunction with
     one of the archive creation operations it instructs ‘tar’ to list
     the member names stored in the archive, as opposed to the actual
     file names.  *Note listing member and file names::.

‘--skip-old-files’

     Do not overwrite existing files when extracting files from an
     archive.  *Note Keep Old Files::.

     This option differs from ‘--keep-old-files’ in that it does not
     treat such files as an error, instead it just silently avoids
     overwriting them.

     The ‘--warning=existing-file’ option can be used together with this
     option to produce warning messages about existing old files (*note
     warnings::).

‘--sort=ORDER’
     Specify the directory sorting order when reading directories.
     ORDER may be one of the following:

     ‘none’
          No directory sorting is performed.  This is the default.

     ‘name’
          Sort the directory entries on name.  The operating system may
          deliver directory entries in a more or less random order, and
          sorting them makes archive creation reproducible.

     ‘inode’
          Sort the directory entries on inode number.  Sorting
          directories on inode number may reduce the amount of disk seek
          operations when creating an archive for some file systems.

‘--sparse’
‘-S’

     Invokes a GNU extension when adding files to an archive that
     handles sparse files efficiently.  *Note sparse::.

‘--sparse-version=VERSION’

     Specifies the “format version” to use when archiving sparse files.
     Implies ‘--sparse’.  *Note sparse::.  For the description of the
     supported sparse formats, *Note Sparse Formats::.

‘--starting-file=NAME’
‘-K NAME’

     This option affects extraction only; ‘tar’ will skip extracting
     files in the archive until it finds one that matches NAME.  *Note
     Scarce::.

‘--strip-components=NUMBER’
     Strip given NUMBER of leading components from file names before
     extraction.  For example, if archive ‘archive.tar’ contained
     ‘/some/file/name’, then running

          tar --extract --file archive.tar --strip-components=2

     would extract this file to file ‘name’.

     *Note transform::.

‘--suffix=SUFFIX’

     Alters the suffix ‘tar’ uses when backing up files from the default
     ‘~’.  *Note backup::.

‘--tape-length=NUM[SUF]’
‘-L NUM[SUF]’

     Specifies the length of tapes that ‘tar’ is writing as being
     NUM x 1024 bytes long.  If optional SUF is given, it specifies a
     multiplicative factor to be used instead of 1024.  For example,
     ‘-L2M’ means 2 megabytes.  *Note Table 9.1: size-suffixes, for a
     list of allowed suffixes.  *Note Using Multiple Tapes::, for a
     detailed discussion of this option.

‘--test-label’

     Reads the volume label.  If an argument is specified, test whether
     it matches the volume label.  *Note --test-label option::.

‘--to-command=COMMAND’

     During extraction ‘tar’ will pipe extracted files to the standard
     input of COMMAND.  *Note Writing to an External Program::.

‘--to-stdout’
‘-O’

     During extraction, ‘tar’ will extract files to stdout rather than
     to the file system.  *Note Writing to Standard Output::.

‘--totals[=SIGNO]’

     Displays the total number of bytes transferred when processing an
     archive.  If an argument is given, these data are displayed on
     request, when signal SIGNO is delivered to ‘tar’.  *Note totals::.

‘--touch’
‘-m’

     Sets the data modification time of extracted files to the
     extraction time, rather than the data modification time stored in
     the archive.  *Note Data Modification Times::.

‘--transform=SED-EXPR’
‘--xform=SED-EXPR’
     Transform file or member names using ‘sed’ replacement expression
     SED-EXPR.  For example,

          $ tar cf archive.tar --transform 's,^\./,usr/,' .

     will add to ‘archive’ files from the current working directory,
     replacing initial ‘./’ prefix with ‘usr/’.  For the detailed
     discussion, *Note transform::.

     To see transformed member names in verbose listings, use
     ‘--show-transformed-names’ option (*note show-transformed-names::).

‘--uncompress’

     (See ‘--compress’, *note gzip::)

‘--ungzip’

     (See ‘--gzip’, *note gzip::)

‘--unlink-first’
‘-U’

     Directs ‘tar’ to remove the corresponding file from the file system
     before extracting it from the archive.  *Note Unlink First::.

‘--unquote’
     Enable unquoting input file or member names (default).  *Note input
     name quoting::.

‘--use-compress-program=PROG’
‘-I=PROG’

     Instructs ‘tar’ to access the archive through PROG, which is
     presumed to be a compression program of some sort.  *Note gzip::.

‘--utc’

     Display file modification dates in UTC.  This option implies
     ‘--verbose’.

‘--verbatim-files-from’

     Instructs GNU ‘tar’ to treat each line read from a file list as a
     file name, even if it starts with a dash.

     File lists are supplied with the ‘--files-from’ (‘-T’) option.  By
     default, each line read from a file list is first trimmed off the
     leading and trailing whitespace and, if the result begins with a
     dash, it is treated as a GNU ‘tar’ command line option.

     Use the ‘--verbatim-files-from’ option to disable this special
     handling.  This facilitates the use of ‘tar’ with file lists
     created by ‘file’ command.

     This option affects all ‘--files-from’ options that occur after it
     in the command line.  Its effect is reverted by the
     ‘--no-verbatim-files-from’ option.

     This option is implied by the ‘--null’ option.

     *Note verbatim-files-from::.

‘--verbose’
‘-v’

     Specifies that ‘tar’ should be more verbose about the operations it
     is performing.  This option can be specified multiple times for
     some operations to increase the amount of information displayed.
     *Note verbose::.

‘--verify’
‘-W’

     Verifies that the archive was correctly written when creating an
     archive.  *Note verify::.

‘--version’

     Print information about the program’s name, version, origin and
     legal status, all on standard output, and then exit successfully.
     *Note help::.

‘--volno-file=FILE’

     Used in conjunction with ‘--multi-volume’.  ‘tar’ will keep track
     of which volume of a multi-volume archive it is working in FILE.
     *Note volno-file::.

‘--warning=KEYWORD’

     Enable or disable warning messages identified by KEYWORD.  The
     messages are suppressed if KEYWORD is prefixed with ‘no-’.  *Note
     warnings::.

‘--wildcards’
     Use wildcards when matching member names with patterns.  *Note
     controlling pattern-matching::.

‘--wildcards-match-slash’
     Wildcards match ‘/’.  *Note controlling pattern-matching::.

‘--xattrs’
     Enable extended attributes support.  *Note xattrs: Extended File
     Attributes.

‘--xattrs-exclude=PATTERN’
     Specify exclude pattern for xattr keys.  *Note xattrs-exclude:
     Extended File Attributes.

‘--xattrs-include=PATTERN.’
     Specify include pattern for xattr keys.  PATTERN is a globbing
     pattern, e.g.  ‘--xattrs-include='user.*'’ to include only
     attributes from the user namespace.  *Note xattrs-include: Extended
     File Attributes.

‘--xz’
‘-J’
     Use ‘xz’ for compressing or decompressing the archives.  *Note
     gzip::.

‘--zstd’
     Use ‘zstd’ for compressing or decompressing the archives.  *Note
     gzip::.

   ---------- Footnotes ----------

   (1) Earlier versions of GNU ‘tar’ understood ‘-l’ as a synonym for
‘--one-file-system’.  The current semantics, which complies to UNIX98,
was introduced with version 1.15.91.  *Note Changes::, for more
information.


File: tar.info,  Node: Short Option Summary,  Next: Position-Sensitive Options,  Prev: Option Summary,  Up: All Options

3.4.3 Short Options Cross Reference
-----------------------------------

Here is an alphabetized list of all of the short option forms, matching
them with the equivalent long option.

Short Option   Reference
               
--------------------------------------------------------------------------
-A             *note --concatenate::.
               
-B             *note --read-full-records::.
               
-C             *note --directory::.
               
-F             *note --info-script::.
               
-G             *note --incremental::.
               
-J             *note --xz::.
               
-K             *note --starting-file::.
               
-L             *note --tape-length::.
               
-M             *note --multi-volume::.
               
-N             *note --newer::.
               
-O             *note --to-stdout::.
               
-P             *note --absolute-names::.
               
-R             *note --block-number::.
               
-S             *note --sparse::.
               
-T             *note --files-from::.
               
-U             *note --unlink-first::.
               
-V             *note --label::.
               
-W             *note --verify::.
               
-X             *note --exclude-from::.
               
-Z             *note --compress::.
               
-b             *note --blocking-factor::.
               
-c             *note --create::.
               
-d             *note --compare::.
               
-f             *note --file::.
               
-g             *note --listed-incremental::.
               
-h             *note --dereference::.
               
-i             *note --ignore-zeros::.
               
-j             *note --bzip2::.
               
-k             *note --keep-old-files::.
               
-l             *note --check-links::.
               
-m             *note --touch::.
               
-o             When extracting, same as *note --no-same-owner::.  When
               creating, – *note --old-archive::.
               
               The latter usage is deprecated.  It is retained for
               compatibility with the earlier versions of GNU ‘tar’.
               In future releases ‘-o’ will be equivalent to
               ‘--no-same-owner’ only.
               
-p             *note --preserve-permissions::.
               
-r             *note --append::.
               
-s             *note --same-order::.
               
-t             *note --list::.
               
-u             *note --update::.
               
-v             *note --verbose::.
               
-w             *note --interactive::.
               
-x             *note --extract::.
               
-z             *note --gzip::.
               


File: tar.info,  Node: Position-Sensitive Options,  Prev: Short Option Summary,  Up: All Options

3.4.4 Position-Sensitive Options
--------------------------------

Some GNU ‘tar’ options can be used multiple times in the same invocation
and affect all arguments that appear after them.  These are options that
control how file names are selected and what kind of pattern matching is
used.

   The most obvious example is the ‘-C’ option.  It instructs ‘tar’ to
change to the directory given as its argument prior to processing the
rest of command line (*note directory::).  Thus, in the following
command:

     tar -c -f a.tar -C /etc passwd -C /var log spool

the file ‘passwd’ will be searched in the directory ‘/etc’, and files
‘log’ and ‘spool’ – in ‘/var’.

   These options can also be used in a file list supplied with the
‘--files-from’ (‘-T’) option (*note files::).  In that case they affect
all files (patterns) appearing in that file after them and remain in
effect for any arguments processed after that file.  For example, if the
file ‘list.txt’ contained:

     README
     -C src
     main.c

and ‘tar’ were invoked as follows:

     tar -c -f a.tar -T list.txt Makefile

then the file ‘README’ would be looked up in the current working
directory, and files ‘main.c’ and ‘Makefile’ would be looked up in the
directory ‘src’.

   Many options can be prefixed with ‘--no-’ to cancel the effect of the
original option.

   For example, the ‘--recursion’ option controls whether to recurse in
the subdirectories.  It’s counterpart ‘--no-recursion’ disables this.
Consider the command below.  It will store in the archive the directory
‘/usr’ with all files and directories that are located in it as well as
any files and directories in ‘/var’, without recursing into them(1):

     tar -cf a.tar --recursion /usr --no-recursion /var/*

   During archive creation, GNU ‘tar’ keeps track of positional options
used and arguments affected by them.  If it finds out that any such
options are used in an obviously erroneous way, the fact is reported and
exit code is set to 2.  E.g.:

     $ tar -cf a.tar . --exclude '*.o'
     tar: The following options were used after any non-optional
     arguments in archive create or update mode.  These options are
     positional and affect only arguments that follow them.  Please,
     rearrange them properly.
     tar: --exclude '*.o' has no effect
     tar: Exiting with failure status due to previous errors

   The following table summarizes all position-sensitive options.

‘--directory=DIR’
‘-C DIR’
     *Note directory::.

‘--null’
‘--no-null’
     *Note nul::.

‘--unquote’
‘--no-unquote’
     *Note input name quoting::.

‘--verbatim-files-from’
‘--no-verbatim-files-from’
     *Note verbatim-files-from::.

‘--recursion’
‘--no-recursion’
     *Note recurse::.

‘--anchored’
‘--no-anchored’
     *Note anchored patterns::.

‘--ignore-case’
‘--no-ignore-case’
     *Note case-insensitive matches::.

‘--wildcards’
‘--no-wildcards’
     *Note controlling pattern-matching::.

‘--wildcards-match-slash’
‘--no-wildcards-match-slash’
     *Note controlling pattern-matching::.

‘--exclude’
     *Note exclude::.

‘--exclude-from’
‘-X’
‘--exclude-caches’
‘--exclude-caches-under’
‘--exclude-caches-all’
‘--exclude-tag’
‘--exclude-ignore’
‘--exclude-ignore-recursive’
‘--exclude-tag-under’
‘--exclude-tag-all’
‘--exclude-vcs’
‘--exclude-vcs-ignores’
‘--exclude-backups’
     *Note exclude::.

   ---------- Footnotes ----------

   (1) The ‘--recursion’ option is the default and is used here for
clarity.  The same example can be written as:

     tar -cf a.tar /usr --no-recursion /var/*


File: tar.info,  Node: help,  Next: defaults,  Prev: All Options,  Up: tar invocation

3.5 GNU ‘tar’ documentation
===========================

Being careful, the first thing is really checking that you are using GNU
‘tar’, indeed.  The ‘--version’ option causes ‘tar’ to print information
about its name, version, origin and legal status, all on standard
output, and then exit successfully.  For example, ‘tar --version’ might
print:

     tar (GNU tar) 1.35
     Copyright (C) 2013-2020 Free Software Foundation, Inc.
     License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
     This is free software: you are free to change and redistribute it.
     There is NO WARRANTY, to the extent permitted by law.

     Written by John Gilmore and Jay Fenlason.

The first occurrence of ‘tar’ in the result above is the program name in
the package (for example, ‘rmt’ is another program), while the second
occurrence of ‘tar’ is the name of the package itself, containing
possibly many programs.  The package is currently named ‘tar’, after the
name of the main program it contains(1).

   Another thing you might want to do is check the spelling or meaning
of some particular ‘tar’ option, without resorting to this manual, once
you have carefully read it.  GNU ‘tar’ has a short help feature,
triggerable through the ‘--help’ option.  By using this option, ‘tar’
will print a usage message listing all available options on standard
output, then exit successfully, without doing anything else and ignoring
all other options.  Even if this is only a brief summary, it may be
several screens long.  So, if you are not using some kind of scrollable
window, you might prefer to use something like:

     $ tar --help | less

presuming, here, that you like using ‘less’ for a pager.  Other popular
pagers are ‘more’ and ‘pg’.  If you know about some KEYWORD which
interests you and do not want to read all the ‘--help’ output, another
common idiom is doing:

     tar --help | grep KEYWORD

for getting only the pertinent lines.  Notice, however, that some ‘tar’
options have long description lines and the above command will list only
the first of them.

   The exact look of the option summary displayed by ‘tar --help’ is
configurable.  *Note Configuring Help Summary::, for a detailed
description.

   If you only wish to check the spelling of an option, running ‘tar
--usage’ may be a better choice.  This will display a terse list of
‘tar’ options without accompanying explanations.

   The short help output is quite succinct, and you might have to get
back to the full documentation for precise points.  If you are reading
this paragraph, you already have the ‘tar’ manual in some form.  This
manual is available in a variety of forms from
<https://www.gnu.org/software/tar/manual>.  It may be printed out of the
GNU ‘tar’ distribution, provided you have TeX already installed
somewhere, and a laser printer around.  Just configure the distribution,
execute the command ‘make dvi’, then print ‘doc/tar.dvi’ the usual way
(contact your local guru to know how).  If GNU ‘tar’ has been
conveniently installed at your place, this manual is also available in
interactive, hypertextual form as an Info file.  Just call ‘info tar’
or, if you do not have the ‘info’ program handy, use the Info reader
provided within GNU Emacs, calling ‘tar’ from the main Info menu.

   Since 2014, GNU ‘tar’ also has a ‘man’ page.  It briefly explains all
the options and operations.  This might be preferable when you don’t
need any background.  But bear in mind that the authoritative source of
information about GNU ‘tar’ is this Texinfo documentation.

   ---------- Footnotes ----------

   (1) There are plans to merge the ‘cpio’ and ‘tar’ packages into a
single one which would be called ‘paxutils’.  So, who knows, one of
these days ‘--version’ might output ‘tar (GNU paxutils) 3.2’.


File: tar.info,  Node: defaults,  Next: verbose,  Prev: help,  Up: tar invocation

3.6 Obtaining GNU ‘tar’ default values
======================================

GNU ‘tar’ has some predefined defaults that are used when you do not
explicitly specify another values.  To obtain a list of such defaults,
use ‘--show-defaults’ option.  This will output the values in the form
of ‘tar’ command line options:

     $ tar --show-defaults
     --format=gnu -f- -b20 --quoting-style=escape
     --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh

Notice, that this option outputs only one line.  The example output
above has been split to fit page boundaries.

The above output shows that this version of GNU ‘tar’ defaults to using
‘gnu’ archive format (*note Formats::), it uses standard output as the
archive, if no ‘--file’ option has been given (*note file tutorial::),
the default blocking factor is 20 (*note Blocking Factor::).  It also
shows the default locations where ‘tar’ will look for ‘rmt’ and ‘rsh’
binaries.


File: tar.info,  Node: verbose,  Next: checkpoints,  Prev: defaults,  Up: tar invocation

3.7 Checking ‘tar’ progress
===========================

Typically, ‘tar’ performs most operations without reporting any
information to the user except error messages.  When using ‘tar’ with
many options, particularly ones with complicated or difficult-to-predict
behavior, it is possible to make serious mistakes.  ‘tar’ provides
several options that make observing ‘tar’ easier.  These options cause
‘tar’ to print information as it progresses in its job, and you might
want to use them just for being more careful about what is going on, or
merely for entertaining yourself.  If you have encountered a problem
when operating on an archive, however, you may need more information
than just an error message in order to solve the problem.  The following
options can be helpful diagnostic tools.

   Normally, the ‘--list’ (‘-t’) command to list an archive prints just
the file names (one per line) and the other commands are silent.  When
used with most operations, the ‘--verbose’ (‘-v’) option causes ‘tar’ to
print the name of each file or archive member as it is processed.  This
and the other options which make ‘tar’ print status information can be
useful in monitoring ‘tar’.

   With ‘--create’ or ‘--extract’, ‘--verbose’ used once just prints the
names of the files or members as they are processed.  Using it twice
causes ‘tar’ to print a longer listing (*Note verbose member listing::,
for the description) for each member.  Since ‘--list’ already prints the
names of the members, ‘--verbose’ used once with ‘--list’ causes ‘tar’
to print an ‘ls -l’ type listing of the files in the archive.  The
following examples both extract members with long list output:

     $ tar --extract --file=archive.tar --verbose --verbose
     $ tar xvvf archive.tar

   Verbose output appears on the standard output except when an archive
is being written to the standard output, as with ‘tar --create --file=-
--verbose’ (‘tar cvf -’, or even ‘tar cv’—if the installer let standard
output be the default archive).  In that case ‘tar’ writes verbose
output to the standard error stream.

   If ‘--index-file=FILE’ is specified, ‘tar’ sends verbose output to
FILE rather than to standard output or standard error.

   The ‘--totals’ option causes ‘tar’ to print on the standard error the
total amount of bytes transferred when processing an archive.  When
creating or appending to an archive, this option prints the number of
bytes written to the archive and the average speed at which they have
been written, e.g.:

     $ tar -c -f archive.tar --totals /home
     Total bytes written: 7924664320 (7.4GiB, 85MiB/s)

   When reading an archive, this option displays the number of bytes
read:

     $ tar -x -f archive.tar --totals
     Total bytes read: 7924664320 (7.4GiB, 95MiB/s)

   Finally, when deleting from an archive, the ‘--totals’ option
displays both numbers plus number of bytes removed from the archive:

     $ tar --delete -f foo.tar --totals --wildcards '*~'
     Total bytes read: 9543680 (9.2MiB, 201MiB/s)
     Total bytes written: 3829760 (3.7MiB, 81MiB/s)
     Total bytes deleted: 1474048

   You can also obtain this information on request.  When ‘--totals’ is
used with an argument, this argument is interpreted as a symbolic name
of a signal, upon delivery of which the statistics is to be printed:

‘--totals=SIGNO’
     Print statistics upon delivery of signal SIGNO.  Valid arguments
     are: ‘SIGHUP’, ‘SIGQUIT’, ‘SIGINT’, ‘SIGUSR1’ and ‘SIGUSR2’.
     Shortened names without ‘SIG’ prefix are also accepted.

   Both forms of ‘--totals’ option can be used simultaneously.  Thus,
‘tar -x --totals --totals=USR1’ instructs ‘tar’ to extract all members
from its default archive and print statistics after finishing the
extraction, as well as when receiving signal ‘SIGUSR1’.

   The ‘--checkpoint’ option prints an occasional message as ‘tar’ reads
or writes the archive.  It is designed for those who don’t need the more
detailed (and voluminous) output of ‘--block-number’ (‘-R’), but do want
visual confirmation that ‘tar’ is actually making forward progress.  By
default it prints a message each 10 records read or written.  This can
be changed by giving it a numeric argument after an equal sign:

     $ tar -c --checkpoint=1000 /var
     tar: Write checkpoint 1000
     tar: Write checkpoint 2000
     tar: Write checkpoint 3000

   This example shows the default checkpoint message used by ‘tar’.  If
you place a dot immediately after the equal sign, it will print a ‘.’ at
each checkpoint(1).  For example:

     $ tar -c --checkpoint=.1000 /var
     ...

   The ‘--checkpoint’ option provides a flexible mechanism for executing
arbitrary actions upon hitting checkpoints, see the next section (*note
checkpoints::), for more information on it.

   The ‘--show-omitted-dirs’ option, when reading an archive—with
‘--list’ or ‘--extract’, for example—causes a message to be printed for
each directory in the archive which is skipped.  This happens regardless
of the reason for skipping: the directory might not have been named on
the command line (implicitly or explicitly), it might be excluded by the
use of the ‘--exclude=PATTERN’ option, or some other reason.

   If ‘--block-number’ (‘-R’) is used, ‘tar’ prints, along with every
message it would normally produce, the block number within the archive
where the message was triggered.  Also, supplementary messages are
triggered when reading blocks full of NULs, or when hitting end of file
on the archive.  As of now, if the archive is properly terminated with a
NUL block, the reading of the file may stop before end of file is met,
so the position of end of file will not usually show when
‘--block-number’ (‘-R’) is used.  Note that GNU ‘tar’ drains the archive
before exiting when reading the archive from a pipe.

   This option is especially useful when reading damaged archives, since
it helps pinpoint the damaged sections.  It can also be used with
‘--list’ (‘-t’) when listing a file-system backup tape, allowing you to
choose among several backup tapes when retrieving a file later, in favor
of the tape where the file appears earliest (closest to the front of the
tape).  *Note backup::.

   ---------- Footnotes ----------

   (1) This is actually a shortcut for ‘--checkpoint=N
--checkpoint-action=dot’.  *Note dot: checkpoints.


File: tar.info,  Node: checkpoints,  Next: warnings,  Prev: verbose,  Up: tar invocation

3.8 Checkpoints
===============

A “checkpoint” is a moment of time before writing Nth record to the
archive (a “write checkpoint”), or before reading Nth record from the
archive (a “read checkpoint”).  Checkpoints allow to periodically
execute arbitrary actions.

   The checkpoint facility is enabled using the following option:

‘--checkpoint[=N]’
     Schedule checkpoints before writing or reading each Nth record.
     The default value for N is 10.

   A list of arbitrary “actions” can be executed at each checkpoint.
These actions include: pausing, displaying textual messages, and
executing arbitrary external programs.  Actions are defined using the
‘--checkpoint-action’ option.

‘--checkpoint-action=ACTION’
     Execute an ACTION at each checkpoint.

   The simplest value of ACTION is ‘echo’.  It instructs ‘tar’ to
display the default message on the standard error stream upon arriving
at each checkpoint.  The default message is (in POSIX locale) ‘Write
checkpoint N’, for write checkpoints, and ‘Read checkpoint N’, for read
checkpoints.  Here, N represents ordinal number of the checkpoint.

   In another locales, translated versions of this message are used.

   This is the default action, so running:

     $ tar -c --checkpoint=1000 --checkpoint-action=echo /var

is equivalent to:

     $ tar -c --checkpoint=1000 /var

   The ‘echo’ action also allows to supply a customized message.  You do
so by placing an equals sign and the message right after it, e.g.:

     --checkpoint-action="echo=Hit %s checkpoint #%u"

   The ‘%s’ and ‘%u’ in the above example are “format specifiers”.  The
‘%s’ specifier is replaced with the “type” of the checkpoint: ‘write’ or
‘read’ (or a corresponding translated version in locales other than
POSIX).  The ‘%u’ specifier is replaced with the ordinal number of the
checkpoint.  Thus, the above example could produce the following output
when used with the ‘--create’ option:

     tar: Hit write checkpoint #10
     tar: Hit write checkpoint #20
     tar: Hit write checkpoint #30

   The complete list of available format specifiers follows.  Some of
them can take optional arguments.  These arguments, if given, are
supplied in curly braces between the percent sign and the specifier
letter.

‘%s’
     Print type of the checkpoint (‘write’ or ‘read’).

‘%u’
     Print number of the checkpoint.

‘%{r,w,d}T’
     Print number of bytes transferred so far and approximate transfer
     speed.  Optional arguments supply prefixes to be used before number
     of bytes read, written and deleted, correspondingly.  If absent,
     they default to ‘R’.  ‘W’, ‘D’.  Any or all of them can be omitted,
     so, that e.g.  ‘%{}T’ means to print corresponding statistics
     without any prefixes.  Any surplus arguments, if present, are
     silently ignored.

          $ tar --delete -f f.tar --checkpoint-action=echo="#%u: %T" main.c
          tar: #1: R: 0 (0B, 0B/s),W: 0 (0B, 0B/s),D: 0
          tar: #2: R: 10240 (10KiB, 19MiB/s),W: 0 (0B, 0B/s),D: 10240

     See also the ‘totals’ action, described below.

‘%{FMT}t’
     Output current local time using FMT as format for ‘strftime’ (*note
     strftime: (strftime(3))strftime.).  The ‘{FMT}’ part is optional.
     If not present, the default format is ‘%c’, i.e.  the preferred
     date and time representation for the current locale.

‘%{N}*’
     Pad output with spaces to the Nth column.  If the ‘{N}’ part is
     omitted, the current screen width is assumed.

‘%c’
     This is a shortcut for ‘%{%Y-%m-%d %H:%M:%S}t: %ds,
     %{read,wrote}T%*\r’, intended mainly for use with ‘ttyout’ action
     (see below).

   Aside from format expansion, the message string is subject to
“unquoting”, during which the backslash “escape sequences” are replaced
with their corresponding ASCII characters (*note escape sequences::).
E.g.  the following action will produce an audible bell and the message
described above at each checkpoint:

     --checkpoint-action='echo=\aHit %s checkpoint #%u'

   There is also a special action which produces an audible signal:
‘bell’.  It is not equivalent to ‘echo='\a'’, because ‘bell’ sends the
bell directly to the console (‘/dev/tty’), whereas ‘echo='\a'’ sends it
to the standard error.

   The ‘ttyout=STRING’ action outputs STRING to ‘/dev/tty’, so it can be
used even if the standard output is redirected elsewhere.  The STRING is
subject to the same modifications as with ‘echo’ action.  In contrast to
the latter, ‘ttyout’ does not prepend ‘tar’ executable name to the
string, nor does it output a newline after it.  For example, the
following action will print the checkpoint message at the same screen
line, overwriting any previous message:

     --checkpoint-action="ttyout=Hit %s checkpoint #%u%*\r"

Notice the use of ‘%*’ specifier to clear out any eventual remains of
the prior output line.  As as more complex example, consider this:

     --checkpoint-action=ttyout='%{%Y-%m-%d %H:%M:%S}t (%d sec): #%u, %T%*\r'

This prints the current local time, number of seconds expired since tar
was started, the checkpoint ordinal number, transferred bytes and
average computed I/O speed.

   Another available checkpoint action is ‘dot’ (or ‘.’).  It instructs
‘tar’ to print a single dot on the standard listing stream, e.g.:

     $ tar -c --checkpoint=1000 --checkpoint-action=dot /var
     ...

   For compatibility with previous GNU ‘tar’ versions, this action can
be abbreviated by placing a dot in front of the checkpoint frequency, as
shown in the previous section.

   The ‘totals’ action prints the total number of bytes transferred so
far.  The format of the data is the same as for the ‘--totals’ option
(*note totals::).  See also ‘%T’ format specifier of the ‘echo’ or
‘ttyout’ action.

   Yet another action, ‘sleep’, pauses ‘tar’ for a specified amount of
seconds.  The following example will stop for 30 seconds at each
checkpoint:

     $ tar -c --checkpoint=1000 --checkpoint-action=sleep=30

   The ‘wait=SIGNO’ action stops further execution until the signal
SIGNO is delivered.  Valid values for SIGNO are: ‘SIGHUP’, ‘SIGQUIT’,
‘SIGINT’, ‘SIGUSR1’ and ‘SIGUSR2’.  The ‘SIG’ prefix is optional.  For
example:

     $ tar -c -f arc --checkpoint=1000 --checkpoint-action wait=USR1 .

   In this example, GNU ‘tar’ will stop archivation at each 1000th
checkpoint.  wait until the ‘SIGUSR1’ signal is delivered, and resume
processing.

   This action is used by the ‘genfile’ utility to perform modifications
on the input files upon hitting certain checkpoints (*note genfile: Exec
Mode.).

   Finally, the ‘exec’ action executes a given external command.  For
example:

     $ tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint

   The supplied command can be any valid command invocation, with or
without additional command line arguments.  If it does contain
arguments, don’t forget to quote it to prevent it from being split by
the shell.  *Note Running External Commands: external, for more detail.

   The command gets a copy of ‘tar’’s environment plus the following
variables:

‘TAR_VERSION’
     GNU ‘tar’ version number.

‘TAR_ARCHIVE’
     The name of the archive ‘tar’ is processing.

‘TAR_BLOCKING_FACTOR’
     Current blocking factor (*note Blocking::).

‘TAR_CHECKPOINT’
     Number of the checkpoint.

‘TAR_SUBCOMMAND’
     A short option describing the operation ‘tar’ is executing.  *Note
     Operations::, for a complete list of subcommand options.

‘TAR_FORMAT’
     Format of the archive being processed.  *Note Formats::, for a
     complete list of archive format names.

   These environment variables can also be passed as arguments to the
command, provided that they are properly escaped, for example:

     tar -c -f arc.tar \
          --checkpoint-action='exec=/sbin/cpoint $TAR_CHECKPOINT'

Notice single quotes to prevent variable names from being expanded by
the shell when invoking ‘tar’.

   Any number of actions can be defined, by supplying several
‘--checkpoint-action’ options in the command line.  For example, the
command below displays two messages, pauses execution for 30 seconds and
executes the ‘/sbin/cpoint’ script:

     $ tar -c -f arc.tar \
            --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
            --checkpoint-action='echo=Sleeping for 30 seconds' \
            --checkpoint-action='sleep=30' \
            --checkpoint-action='exec=/sbin/cpoint'

   This example also illustrates the fact that ‘--checkpoint-action’ can
be used without ‘--checkpoint’.  In this case, the default checkpoint
frequency (at each 10th record) is assumed.


File: tar.info,  Node: warnings,  Next: interactive,  Prev: checkpoints,  Up: tar invocation

3.9 Controlling Warning Messages
================================

Sometimes, while performing the requested task, GNU ‘tar’ notices some
conditions that are not exactly errors, but which the user should be
aware of.  When this happens, ‘tar’ issues a “warning message”
describing the condition.  Warning messages are output to the standard
error and they do not affect the exit code of ‘tar’ command.

   GNU ‘tar’ allows the user to suppress some or all of its warning
messages:

‘--warning=KEYWORD’
     Control display of the warning messages identified by KEYWORD.  If
     KEYWORD starts with the prefix ‘no-’, such messages are suppressed.
     Otherwise, they are enabled.

     Multiple ‘--warning’ options accumulate.

   By default, GNU ‘tar’ enables all messages, except those that are
enabled in verbose mode (*note verbose tutorial::).  *Note Warning
Defaults::, for details.

   The subsections below discuss allowed values for KEYWORD along with
the warning messages they control.

* Menu:

* General Warnings::  Keywords applicable for ‘tar --create’.
* Archive Creation Warnings:: Keywords applicable for ‘tar --create’.
* Archive Extraction Warnings:: Keywords applicable for ‘tar --extract’.
* Incremental Extraction Warnings:: Keywords controlling incremental extraction.
* Warning Classes:: Convenience keywords control multiple warnings.
* Warning Defaults:: Default settings for warnings.


File: tar.info,  Node: General Warnings,  Next: Archive Creation Warnings,  Up: warnings

3.9.1 Keywords controlling ‘tar’ operation
------------------------------------------

These keywords control warnings that may appear in any GNU ‘tar’
operation mode:

 -- warning: filename-with-nuls
     ‘file name read contains nul character’

 -- warning: filename-with-nuls
     ‘%s: file name read contains nul character’

 -- warning: alone-zero-block
     ‘A lone zero block at %s’.  Notice, that this warning is suppressed
     if ‘--ignore-zeros’ is in effect (*note Ignore Zeros::).

 -- warning: missing-zero-blocks
     ‘Terminating zero blocks missing at %s’.  This warning is
     suppressed if ‘--ignore-zeros’ is in effect (*note Ignore Zeros::).


File: tar.info,  Node: Archive Creation Warnings,  Next: Archive Extraction Warnings,  Prev: General Warnings,  Up: warnings

3.9.2 Keywords applicable for ‘tar --create’
--------------------------------------------

The following keywords control messages that can be issued while
creating archives.

 -- warning: cachedir
     ‘%s: contains a cache directory tag %s; %s’

 -- warning: file-shrank
     ‘%s: File shrank by %s bytes; padding with zeros’

 -- warning: xdev
     ‘%s: file is on a different filesystem; not dumped’

 -- warning: file-ignored
     ‘%s: Unknown file type; file ignored’
     ‘%s: socket ignored’
     ‘%s: door ignored’

 -- warning: file-unchanged
     ‘%s: file is unchanged; not dumped’

 -- warning: ignore-archive
     ‘%s: archive cannot contain itself; not dumped’

 -- warning: file-removed
     ‘%s: File removed before we read it’

 -- warning: file-changed
     ‘%s: file changed as we read it’

     Suppresses warnings about read failures, which can occur if files
     or directories are unreadable, or if they change while being read.
     This keyword applies only if used together with the
     ‘--ignore-failed-read’ option.  *Note Ignore Failed Read::.


File: tar.info,  Node: Archive Extraction Warnings,  Next: Incremental Extraction Warnings,  Prev: Archive Creation Warnings,  Up: warnings

3.9.3 Keywords applicable for ‘tar --extract’
---------------------------------------------

The following keywords control warnings that can be issued during
archive extraction.

 -- warning: existing-file
     ‘%s: skipping existing file’

 -- warning: timestamp
     ‘%s: implausibly old time stamp %s’
     ‘%s: time stamp %s is %s s in the future’

 -- warning: contiguous-cast
     ‘Extracting contiguous files as regular files’

 -- warning: symlink-cast
     ‘Attempting extraction of symbolic links as hard links’, warning
     message ‘Attempting extraction of symbolic links as hard links’

 -- warning: unknown-cast
     ‘%s: Unknown file type '%c', extracted as normal file’

 -- warning: ignore-newer
     ‘Current %s is newer or same age’

 -- warning: unknown-keyword
     ‘Ignoring unknown extended header keyword '%s'’

 -- warning: decompress-program
     Controls verbose description of failures occurring when trying to
     run alternative decompressor programs (*note alternative
     decompression programs::).  This warning is disabled by default
     (unless ‘--verbose’ is used).  A common example of what you can get
     when using this warning is:

          $ tar --warning=decompress-program -x -f archive.Z
          tar (child): cannot run compress: No such file or directory
          tar (child): trying gzip

     This means that ‘tar’ first tried to decompress ‘archive.Z’ using
     ‘compress’, and, when that failed, switched to ‘gzip’.

 -- warning: record-size
     ‘Record size = %lu blocks’


File: tar.info,  Node: Incremental Extraction Warnings,  Next: Warning Classes,  Prev: Archive Extraction Warnings,  Up: warnings

3.9.4 Keywords controlling incremental extraction
-------------------------------------------------

These keywords control warnings that may appear when extracting from
incremental archives.

 -- warning: rename-directory
     ‘%s: Directory has been renamed from %s’
     ‘%s: Directory has been renamed’

 -- warning: new-directory
     ‘%s: Directory is new’

 -- warning: xdev
     ‘%s: directory is on a different device: not purging’

 -- warning: bad-dumpdir
     ‘Malformed dumpdir: 'X' never used’


File: tar.info,  Node: Warning Classes,  Next: Warning Defaults,  Prev: Incremental Extraction Warnings,  Up: warnings

3.9.5 Warning Classes
---------------------

These convenience keywords define “warning classes”.  When used, they
affect several warnings at once.

 -- warning: all
     Enable all warning messages.

 -- warning: none
     Disable all warning messages.

 -- warning: verbose
     A shorthand for all messages enabled when ‘--verbose’ (*note
     verbose tutorial::) is in effect.  These are: ‘decompress-program’,
     ‘existing-file’, ‘new-directory’, ‘record-size’,
     ‘rename-directory’.


File: tar.info,  Node: Warning Defaults,  Prev: Warning Classes,  Up: warnings

3.9.6 Default Warning Settings
------------------------------

GNU ‘tar’ default settings correspond to:

     --warning=all --warning=no-verbose --warning=no-missing-zero-blocks


File: tar.info,  Node: interactive,  Next: external,  Prev: warnings,  Up: tar invocation

3.10 Asking for Confirmation During Operations
==============================================

Typically, ‘tar’ carries out a command without stopping for further
instructions.  In some situations however, you may want to exclude some
files and archive members from the operation (for instance if disk or
storage space is tight).  You can do this by excluding certain files
automatically (*note Choosing::), or by performing an operation
interactively, using the ‘--interactive’ (‘-w’) option.  ‘tar’ also
accepts ‘--confirmation’ for this option.

   When the ‘--interactive’ (‘-w’) option is specified, before reading,
writing, or deleting files, ‘tar’ first prints a message for each such
file, telling what operation it intends to take, then asks for
confirmation on the terminal.  The actions which require confirmation
include adding a file to the archive, extracting a file from the
archive, deleting a file from the archive, and deleting a file from
disk.  To confirm the action, you must type a line of input beginning
with ‘y’.  If your input line begins with anything other than ‘y’, ‘tar’
skips that file.

   If ‘tar’ is reading the archive from the standard input, ‘tar’ opens
the file ‘/dev/tty’ to support the interactive communications.

   Verbose output is normally sent to standard output, separate from
other error messages.  However, if the archive is produced directly on
standard output, then verbose output is mixed with errors on ‘stderr’.
Producing the archive on standard output may be used as a way to avoid
using disk space, when the archive is soon to be consumed by another
process reading it, say.  Some people felt the need of producing an
archive on stdout, still willing to segregate between verbose output and
error output.  A possible approach would be using a named pipe to
receive the archive, and having the consumer process to read from that
named pipe.  This has the advantage of letting standard output free to
receive verbose output, all separate from errors.


File: tar.info,  Node: external,  Prev: interactive,  Up: tar invocation

3.11 Running External Commands
==============================

Certain GNU ‘tar’ operations imply running external commands that you
supply on the command line.  One of such operations is checkpointing,
described above (*note checkpoint exec::).  Another example of this
feature is the ‘-I’ option, which allows you to supply the program to
use for compressing or decompressing the archive (*note
use-compress-program::).

   Whenever such operation is requested, ‘tar’ first splits the supplied
command into words much like the shell does.  It then treats the first
word as the name of the program or the shell script to execute and the
rest of words as its command line arguments.  The program, unless given
as an absolute file name, is searched in the shell’s ‘PATH’.

   Any additional information is normally supplied to external commands
in environment variables, specific to each particular operation.  For
example, the ‘--checkpoint-action=exec’ option, defines the
‘TAR_ARCHIVE’ variable to the name of the archive being worked upon.
You can, should the need be, use these variables in the command line of
the external command.  For example:

     $ tar -x -f archive.tar \
         --checkpoint-action=exec='printf "%04d in %32s\r" $TAR_CHECKPOINT $TAR_ARCHIVE'

This command prints for each checkpoint its number and the name of the
archive, using the same output line on the screen.

   Notice the use of single quotes to prevent variable names from being
expanded by the shell when invoking ‘tar’.


File: tar.info,  Node: operations,  Next: Backups,  Prev: tar invocation,  Up: Top

4 GNU ‘tar’ Operations
**********************

* Menu:

* Basic tar::
* Advanced tar::
* create options::
* extract options::
* backup::
* looking ahead::


File: tar.info,  Node: Basic tar,  Next: Advanced tar,  Up: operations

4.1 Basic GNU ‘tar’ Operations
==============================

The basic ‘tar’ operations, ‘--create’ (‘-c’), ‘--list’ (‘-t’) and
‘--extract’ (‘--get’, ‘-x’), are currently presented and described in
the tutorial chapter of this manual.  This section provides some
complementary notes for these operations.

‘--create’
‘-c’

     Creating an empty archive would have some kind of elegance.  One
     can initialize an empty archive and later use ‘--append’ (‘-r’) for
     adding all members.  Some applications would not welcome making an
     exception in the way of adding the first archive member.  On the
     other hand, many people reported that it is dangerously too easy
     for ‘tar’ to destroy a magnetic tape with an empty archive(1).  The
     two most common errors are:

       1. Mistakingly using ‘create’ instead of ‘extract’, when the
          intent was to extract the full contents of an archive.  This
          error is likely: keys ‘c’ and ‘x’ are right next to each other
          on the QWERTY keyboard.  Instead of being unpacked, the
          archive then gets wholly destroyed.  When users speak about
          “exploding” an archive, they usually mean something else :-).

       2. Forgetting the argument to ‘file’, when the intent was to
          create an archive with a single file in it.  This error is
          likely because a tired user can easily add the ‘f’ key to the
          cluster of option letters, by the mere force of habit, without
          realizing the full consequence of doing so.  The usual
          consequence is that the single file, which was meant to be
          saved, is rather destroyed.

     So, recognizing the likelihood and the catastrophic nature of these
     errors, GNU ‘tar’ now takes some distance from elegance, and
     cowardly refuses to create an archive when ‘--create’ option is
     given, there are no arguments besides options, and ‘--files-from’
     (‘-T’) option is _not_ used.  To get around the cautiousness of GNU
     ‘tar’ and nevertheless create an archive with nothing in it, one
     may still use, as the value for the ‘--files-from’ option, a file
     with no names in it, as shown in the following commands:

          tar --create --file=empty-archive.tar --files-from=/dev/null
          tar -cf empty-archive.tar -T /dev/null

‘--extract’
‘--get’
‘-x’

     A socket is stored, within a GNU ‘tar’ archive, as a pipe.

‘--list (-t)’

     GNU ‘tar’ now shows dates as ‘1996-08-30’, while it used to show
     them as ‘Aug 30 1996’.  Preferably, people should get used to ISO
     8601 dates.  Local American dates should be made available again
     with full date localization support, once ready.  In the meantime,
     programs not being localizable for dates should prefer
     international dates, that’s really the way to go.

     Look up <http://www.cl.cam.ac.uk/~mgk25/iso-time.html> if you are
     curious, it contains a detailed explanation of the ISO 8601
     standard.

   ---------- Footnotes ----------

   (1) This is well described in ‘Unix-haters Handbook’, by Simson
Garfinkel, Daniel Weise & Steven Strassmann, IDG Books, ISBN
1-56884-203-1.


File: tar.info,  Node: Advanced tar,  Next: create options,  Prev: Basic tar,  Up: operations

4.2 Advanced GNU ‘tar’ Operations
=================================

Now that you have learned the basics of using GNU ‘tar’, you may want to
learn about further ways in which ‘tar’ can help you.

   This chapter presents five, more advanced operations which you
probably won’t use on a daily basis, but which serve more specialized
functions.  We also explain the different styles of options and why you
might want to use one or another, or a combination of them in your ‘tar’
commands.  Additionally, this chapter includes options which allow you
to define the output from ‘tar’ more carefully, and provide help and
error correction in special circumstances.

* Menu:

* Operations::
* append::
* update::
* concatenate::
* delete::
* compare::


File: tar.info,  Node: Operations,  Next: append,  Up: Advanced tar

4.2.1 The Five Advanced ‘tar’ Operations
----------------------------------------

In the last chapter, you learned about the first three operations to
‘tar’.  This chapter presents the remaining five operations to ‘tar’:
‘--append’, ‘--update’, ‘--concatenate’, ‘--delete’, and ‘--compare’.

   You are not likely to use these operations as frequently as those
covered in the last chapter; however, since they perform specialized
functions, they are quite useful when you do need to use them.  We will
give examples using the same directory and files that you created in the
last chapter.  As you may recall, the directory is called ‘practice’,
the files are ‘jazz’, ‘blues’, ‘folk’, and the two archive files you
created are ‘collection.tar’ and ‘music.tar’.

   We will also use the archive files ‘afiles.tar’ and ‘bfiles.tar’.
The archive ‘afiles.tar’ contains the members ‘apple’, ‘angst’, and
‘aspic’; ‘bfiles.tar’ contains the members ‘./birds’, ‘baboon’, and
‘./box’.

   Unless we state otherwise, all practicing you do and examples you
follow in this chapter will take place in the ‘practice’ directory that
you created in the previous chapter; see *note prepare for examples::.
(Below in this section, we will remind you of the state of the examples
where the last chapter left them.)

   The five operations that we will cover in this chapter are:

‘--append’
‘-r’
     Add new entries to an archive that already exists.
‘--update’
‘-u’
     Add more recent copies of archive members to the end of an archive,
     if they exist.
‘--concatenate’
‘--catenate’
‘-A’
     Add one or more pre-existing archives to the end of another
     archive.
‘--delete’
     Delete items from an archive (does not work on tapes).
‘--compare’
‘--diff’
‘-d’
     Compare archive members to their counterparts in the file system.


File: tar.info,  Node: append,  Next: update,  Prev: Operations,  Up: Advanced tar

4.2.2 How to Add Files to Existing Archives: ‘--append’
-------------------------------------------------------

If you want to add files to an existing archive, you don’t need to
create a new archive; you can use ‘--append’ (‘-r’).  The archive must
already exist in order to use ‘--append’.  (A related operation is the
‘--update’ operation; you can use this to add newer versions of archive
members to an existing archive.  To learn how to do this with
‘--update’, *note update::.)

   If you use ‘--append’ to add a file that has the same name as an
archive member to an archive containing that archive member, then the
old member is not deleted.  What does happen, however, is somewhat
complex.  ‘tar’ _allows_ you to have infinite number of files with the
same name.  Some operations treat these same-named members no
differently than any other set of archive members: for example, if you
view an archive with ‘--list’ (‘-t’), you will see all of those members
listed, with their data modification times, owners, etc.

   Other operations don’t deal with these members as perfectly as you
might prefer; if you were to use ‘--extract’ to extract the archive,
only the most recently added copy of a member with the same name as
other members would end up in the working directory.  This is because
‘--extract’ extracts an archive in the order the members appeared in the
archive; the most recently archived members will be extracted last.
Additionally, an extracted member will _replace_ a file of the same name
which existed in the directory already, and ‘tar’ will not prompt you
about this(1).  Thus, only the most recently archived member will end up
being extracted, as it will replace the one extracted before it, and so
on.

   There exists a special option that allows you to get around this
behavior and extract (or list) only a particular copy of the file.  This
is ‘--occurrence’ option.  If you run ‘tar’ with this option, it will
extract only the first copy of the file.  You may also give this option
an argument specifying the number of copy to be extracted.  Thus, for
example if the archive ‘archive.tar’ contained three copies of file
‘myfile’, then the command

     tar --extract --file archive.tar --occurrence=2 myfile

would extract only the second copy.  *Note —occurrence: Option Summary,
for the description of ‘--occurrence’ option.

   If you want to replace an archive member, use ‘--delete’ to delete
the member you want to remove from the archive, and then use ‘--append’
to add the member you want to be in the archive.  Note that you can not
change the order of the archive; the most recently added member will
still appear last.  In this sense, you cannot truly “replace” one member
with another.  (Replacing one member with another will not work on
certain types of media, such as tapes; see *note delete:: and *note
Media::, for more information.)

* Menu:

* appending files::             Appending Files to an Archive
* multiple::

   ---------- Footnotes ----------

   (1) Unless you give it ‘--keep-old-files’ (or ‘--skip-old-files’)
option, or the disk copy is newer than the one in the archive and you
invoke ‘tar’ with ‘--keep-newer-files’ option.


File: tar.info,  Node: appending files,  Next: multiple,  Up: append

4.2.2.1 Appending Files to an Archive
.....................................

The simplest way to add a file to an already existing archive is the
‘--append’ (‘-r’) operation, which writes specified files into the
archive whether or not they are already among the archived files.

   When you use ‘--append’, you _must_ specify file name arguments, as
there is no default.  If you specify a file that already exists in the
archive, another copy of the file will be added to the end of the
archive.  As with other operations, the member names of the newly added
files will be exactly the same as their names given on the command line.
The ‘--verbose’ (‘-v’) option will print out the names of the files as
they are written into the archive.

   ‘--append’ cannot be performed on some tape drives, unfortunately,
due to deficiencies in the formats those tape drives use.  The archive
must be a valid ‘tar’ archive, or else the results of using this
operation will be unpredictable.  *Note Media::.

   To demonstrate using ‘--append’ to add a file to an archive, create a
file called ‘rock’ in the ‘practice’ directory.  Make sure you are in
the ‘practice’ directory.  Then, run the following ‘tar’ command to add
‘rock’ to ‘collection.tar’:

     $ tar --append --file=collection.tar rock

If you now use the ‘--list’ (‘-t’) operation, you will see that ‘rock’
has been added to the archive:

     $ tar --list --file=collection.tar
     -rw-r--r-- me/user          28 1996-10-18 16:31 jazz
     -rw-r--r-- me/user          21 1996-09-23 16:44 blues
     -rw-r--r-- me/user          20 1996-09-23 16:44 folk
     -rw-r--r-- me/user          20 1996-09-23 16:44 rock


File: tar.info,  Node: multiple,  Prev: appending files,  Up: append

4.2.2.2 Multiple Members with the Same Name
...........................................

You can use ‘--append’ (‘-r’) to add copies of files which have been
updated since the archive was created.  (However, we do not recommend
doing this since there is another ‘tar’ option called ‘--update’; *Note
update::, for more information.  We describe this use of ‘--append’ here
for the sake of completeness.)  When you extract the archive, the older
version will be effectively lost.  This works because files are
extracted from an archive in the order in which they were archived.
Thus, when the archive is extracted, a file archived later in time will
replace a file of the same name which was archived earlier, even though
the older version of the file will remain in the archive unless you
delete all versions of the file.

   Supposing you change the file ‘blues’ and then append the changed
version to ‘collection.tar’.  As you saw above, the original ‘blues’ is
in the archive ‘collection.tar’.  If you change the file and append the
new version of the file to the archive, there will be two copies in the
archive.  When you extract the archive, the older version of the file
will be extracted first, and then replaced by the newer version when it
is extracted.

   You can append the new, changed copy of the file ‘blues’ to the
archive in this way:

     $ tar --append --verbose --file=collection.tar blues
     blues

Because you specified the ‘--verbose’ option, ‘tar’ has printed the name
of the file being appended as it was acted on.  Now list the contents of
the archive:

     $ tar --list --verbose --file=collection.tar
     -rw-r--r-- me/user          28 1996-10-18 16:31 jazz
     -rw-r--r-- me/user          21 1996-09-23 16:44 blues
     -rw-r--r-- me/user          20 1996-09-23 16:44 folk
     -rw-r--r-- me/user          20 1996-09-23 16:44 rock
     -rw-r--r-- me/user          58 1996-10-24 18:30 blues

The newest version of ‘blues’ is now at the end of the archive (note the
different creation dates and file sizes).  If you extract the archive,
the older version of the file ‘blues’ will be replaced by the newer
version.  You can confirm this by extracting the archive and running
‘ls’ on the directory.

   If you wish to extract the first occurrence of the file ‘blues’ from
the archive, use ‘--occurrence’ option, as shown in the following
example:

     $ tar --extract -vv --occurrence --file=collection.tar blues
     -rw-r--r-- me/user          21 1996-09-23 16:44 blues

   *Note Writing::, for more information on ‘--extract’ and see *note
–occurrence: Option Summary, for a description of ‘--occurrence’ option.


File: tar.info,  Node: update,  Next: concatenate,  Prev: append,  Up: Advanced tar

4.2.3 Updating an Archive
-------------------------

In the previous section, you learned how to use ‘--append’ to add a file
to an existing archive.  A related operation is ‘--update’ (‘-u’).  The
‘--update’ operation updates a ‘tar’ archive by comparing the date of
the specified archive members against the date of the file with the same
name.  If the file has been modified more recently than the archive
member, then the newer version of the file is added to the archive (as
with ‘--append’).

   Unfortunately, you cannot use ‘--update’ with magnetic tape drives.
The operation will fail.

   Both ‘--update’ and ‘--append’ work by adding to the end of the
archive.  When you extract a file from the archive, only the version
stored last will wind up in the file system, unless you use the
‘--backup’ option.  *Note multiple::, for a detailed discussion.

* Menu:

* how to update::


File: tar.info,  Node: how to update,  Up: update

4.2.3.1 How to Update an Archive Using ‘--update’
.................................................

You must use file name arguments with the ‘--update’ (‘-u’) operation.
If you don’t specify any files, ‘tar’ won’t act on any files and won’t
tell you that it didn’t do anything (which may end up confusing you).

   To see the ‘--update’ option at work, create a new file, ‘classical’,
in your practice directory, and some extra text to the file ‘blues’,
using any text editor.  Then invoke ‘tar’ with the ‘update’ operation
and the ‘--verbose’ (‘-v’) option specified, using the names of all the
files in the ‘practice’ directory as file name arguments:

     $ tar --update -v -f collection.tar blues folk rock classical
     blues
     classical
     $

Because we have specified verbose mode, ‘tar’ prints out the names of
the files it is working on, which in this case are the names of the
files that needed to be updated.  If you run ‘tar --list’ and look at
the archive, you will see ‘blues’ and ‘classical’ at its end.  There
will be a total of two versions of the member ‘blues’; the one at the
end will be newer and larger, since you added text before updating it.

   The reason ‘tar’ does not overwrite the older file when updating it
is that writing to the middle of a section of tape is a difficult
process.  Tapes are not designed to go backward.  *Note Media::, for
more information about tapes.

   ‘--update’ (‘-u’) is not suitable for performing backups for two
reasons: it does not change directory content entries, and it lengthens
the archive every time it is used.  The GNU ‘tar’ options intended
specifically for backups are more efficient.  If you need to run
backups, please consult *note Backups::.


File: tar.info,  Node: concatenate,  Next: delete,  Prev: update,  Up: Advanced tar

4.2.4 Combining Archives with ‘--concatenate’
---------------------------------------------

Sometimes it may be convenient to add a second archive onto the end of
an archive rather than adding individual files to the archive.  To add
one or more archives to the end of another archive, you should use the
‘--concatenate’ (‘--catenate’, ‘-A’) operation.

   To use ‘--concatenate’, give the first archive with ‘--file’ option
and name the rest of archives to be concatenated on the command line.
The members, and their member names, will be copied verbatim from those
archives to the first one(1).  The new, concatenated archive will be
called by the same name as the one given with the ‘--file’ option.  As
usual, if you omit ‘--file’, ‘tar’ will use the value of the environment
variable ‘TAPE’, or, if this has not been set, the default archive name.

   To demonstrate how ‘--concatenate’ works, create two small archives
called ‘bluesrock.tar’ and ‘folkjazz.tar’, using the relevant files from
‘practice’:

     $ tar -cvf bluesrock.tar blues rock
     blues
     rock
     $ tar -cvf folkjazz.tar folk jazz
     folk
     jazz

If you like, you can run ‘tar --list’ to make sure the archives contain
what they are supposed to:

     $ tar -tvf bluesrock.tar
     -rw-r--r-- melissa/user    105 1997-01-21 19:42 blues
     -rw-r--r-- melissa/user     33 1997-01-20 15:34 rock
     $ tar -tvf jazzfolk.tar
     -rw-r--r-- melissa/user     20 1996-09-23 16:44 folk
     -rw-r--r-- melissa/user     65 1997-01-30 14:15 jazz

   We can concatenate these two archives with ‘tar’:

     $ tar --concatenate --file=bluesrock.tar jazzfolk.tar

   If you now list the contents of the ‘bluesrock.tar’, you will see
that now it also contains the archive members of ‘jazzfolk.tar’:

     $ tar --list --file=bluesrock.tar
     blues
     rock
     folk
     jazz

   When you use ‘--concatenate’, the source and target archives must
already exist and must have been created using compatible format
parameters.  Notice, that ‘tar’ does not check whether the archives it
concatenates have compatible formats, it does not even check if the
files are really tar archives.

   Like ‘--append’ (‘-r’), this operation cannot be performed on some
tape drives, due to deficiencies in the formats those tape drives use.

   It may seem more intuitive to you to want or try to use ‘cat’ to
concatenate two archives instead of using the ‘--concatenate’ operation;
after all, ‘cat’ is the utility for combining files.

   However, ‘tar’ archives incorporate an end-of-file marker which must
be removed if the concatenated archives are to be read properly as one
archive.  ‘--concatenate’ removes the end-of-archive marker from the
target archive before each new archive is appended.  If you use ‘cat’ to
combine the archives, the result will not be a valid ‘tar’ format
archive.  If you need to retrieve files from an archive that was added
to using the ‘cat’ utility, use the ‘--ignore-zeros’ (‘-i’) option.
*Note Ignore Zeros::, for further information on dealing with archives
improperly combined using the ‘cat’ shell utility.

   ---------- Footnotes ----------

   (1) This can cause multiple members to have the same name.  For
information on how this affects reading the archive, see *note
multiple::.


File: tar.info,  Node: delete,  Next: compare,  Prev: concatenate,  Up: Advanced tar

4.2.5 Removing Archive Members Using ‘--delete’
-----------------------------------------------

You can remove members from an archive by using the ‘--delete’ option.
Specify the name of the archive with ‘--file’ (‘-f’) and then specify
the names of the members to be deleted; if you list no member names,
nothing will be deleted.  The ‘--verbose’ option will cause ‘tar’ to
print the names of the members as they are deleted.  As with
‘--extract’, you must give the exact member names when using ‘tar
--delete’.  ‘--delete’ will remove all versions of the named file from
the archive.  The ‘--delete’ operation can run very slowly.

   Unlike other operations, ‘--delete’ has no short form.

   This operation will rewrite the archive.  You can only use ‘--delete’
on an archive if the archive device allows you to write to any point on
the media, such as a disk; because of this, it does not work on magnetic
tapes.  Do not try to delete an archive member from a magnetic tape; the
action will not succeed, and you will be likely to scramble the archive
and damage your tape.  There is no safe way (except by completely
re-writing the archive) to delete files from most kinds of magnetic
tape.  *Note Media::.

   To delete all versions of the file ‘blues’ from the archive
‘collection.tar’ in the ‘practice’ directory, make sure you are in that
directory, and then,

     $ tar --list --file=collection.tar
     blues
     folk
     jazz
     rock
     $ tar --delete --file=collection.tar blues
     $ tar --list --file=collection.tar
     folk
     jazz
     rock

   The ‘--delete’ option has been reported to work properly when ‘tar’
acts as a filter from ‘stdin’ to ‘stdout’.


File: tar.info,  Node: compare,  Prev: delete,  Up: Advanced tar

4.2.6 Comparing Archive Members with the File System
----------------------------------------------------

The ‘--compare’ (‘-d’), or ‘--diff’ operation compares specified archive
members against files with the same names, and then reports differences
in file size, mode, owner, modification date and contents.  You should
_only_ specify archive member names, not file names.  If you do not name
any members, then ‘tar’ will compare the entire archive.  If a file is
represented in the archive but does not exist in the file system, ‘tar’
reports a difference.

   You have to specify the record size of the archive when modifying an
archive with a non-default record size.

   ‘tar’ ignores files in the file system that do not have corresponding
members in the archive.

   The following example compares the archive members ‘rock’, ‘blues’
and ‘funk’ in the archive ‘bluesrock.tar’ with files of the same name in
the file system.  (Note that there is no file, ‘funk’; ‘tar’ will report
an error message.)

     $ tar --compare --file=bluesrock.tar rock blues funk
     rock
     blues
     tar: funk not found in archive

   The spirit behind the ‘--compare’ (‘--diff’, ‘-d’) option is to check
whether the archive represents the current state of files on disk, more
than validating the integrity of the archive media.  For this latter
goal, see *note verify::.


File: tar.info,  Node: create options,  Next: extract options,  Prev: Advanced tar,  Up: operations

4.3 Options Used by ‘--create’
==============================

The previous chapter described the basics of how to use ‘--create’
(‘-c’) to create an archive from a set of files.  *Note create::.  This
section described advanced options to be used with ‘--create’.

* Menu:

* override::                  Overriding File Metadata.
* Extended File Attributes::
* Ignore Failed Read::


File: tar.info,  Node: override,  Next: Extended File Attributes,  Up: create options

4.3.1 Overriding File Metadata
------------------------------

As described above, a ‘tar’ archive keeps, for each member it contains,
its “metadata”, such as modification time, mode and ownership of the
file.  GNU ‘tar’ allows to replace these data with other values when
adding files to the archive.  The options described in this section
affect creation of archives of any type.  For POSIX archives, see also
*note PAX keywords::, for additional ways of controlling metadata,
stored in the archive.

‘--mode=PERMISSIONS’

     When adding files to an archive, ‘tar’ will use PERMISSIONS for the
     archive members, rather than the permissions from the files.
     PERMISSIONS can be specified either as an octal number or as
     symbolic permissions, like with ‘chmod’ (*Note Permissions:
     (fileutils)File permissions.  This reference also has useful
     information for those not being overly familiar with the UNIX
     permission system).  Using latter syntax allows for more
     flexibility.  For example, the value ‘a+rw’ adds read and write
     permissions for everybody, while retaining executable bits on
     directories or on any other file already marked as executable:

          $ tar -c -f archive.tar --mode='a+rw' .

‘--mtime=DATE’

     When adding files to an archive, ‘tar’ will use DATE as the
     modification time of members when creating archives, instead of
     their actual modification times.  The argument DATE can be either a
     textual date representation in almost arbitrary format (*note Date
     input formats::) or a name of an existing file, starting with ‘/’
     or ‘.’.  In the latter case, the modification time of that file
     will be used.

     The following example will set the modification date to 00:00:00,
     January 1, 1970:

          $ tar -c -f archive.tar --mtime='1970-01-01' .

     When used with ‘--verbose’ (*note verbose tutorial::) GNU ‘tar’
     will try to convert the specified date back to its textual
     representation and compare it with the one given with ‘--mtime’
     options.  If the two dates differ, ‘tar’ will print a warning
     saying what date it will use.  This is to help user ensure he is
     using the right date.

     For example:

          $ tar -c -f archive.tar -v --mtime=yesterday .
          tar: Option --mtime: Treating date 'yesterday' as 2006-06-20
          13:06:29.152478
          ...

     When used with ‘--clamp-mtime’ GNU ‘tar’ will only set the
     modification date to DATE on files whose actual modification date
     is later than DATE.  This is to make it easy to build reproducible
     archives given a common timestamp for generated files while still
     retaining the original timestamps of untouched files.

          $ tar -c -f archive.tar --clamp-mtime --mtime=@$SOURCE_DATE_EPOCH .

‘--owner=USER’

     Specifies that ‘tar’ should use USER as the owner of members when
     creating archives, instead of the user associated with the source
     file.

     If USER contains a colon, it is taken to be of the form NAME:ID
     where a nonempty NAME specifies the user name and a nonempty ID
     specifies the decimal numeric user ID.  If USER does not contain a
     colon, it is taken to be a user number if it is one or more decimal
     digits; otherwise it is taken to be a user name.

     If a name is given but no number, the number is inferred from the
     current host’s user database if possible, and the file’s user
     number is used otherwise.  If a number is given but no name, the
     name is inferred from the number if possible, and an empty name is
     used otherwise.  If both name and number are given, the user
     database is not consulted, and the name and number need not be
     valid on the current host.

     There is no value indicating a missing number, and ‘0’ usually
     means ‘root’.  Some people like to force ‘0’ as the value to offer
     in their distributions for the owner of files, because the ‘root’
     user is anonymous anyway, so that might as well be the owner of
     anonymous archives.  For example:

          $ tar -c -f archive.tar --owner=0 .

     or:

          $ tar -c -f archive.tar --owner=root .

‘--group=GROUP’

     Files added to the ‘tar’ archive will have a group ID of GROUP,
     rather than the group from the source file.  As with ‘--owner’, the
     argument GROUP can be an existing group symbolic name, or a decimal
     numeric group ID, or NAME:ID.

   The ‘--owner’ and ‘--group’ options affect all files added to the
archive.  GNU ‘tar’ provides also two options that allow for more
detailed control over owner translation:

‘--owner-map=FILE’
     Read UID translation map from FILE.

     When reading, empty lines are ignored.  The ‘#’ sign, unless
     quoted, introduces a comment, which extends to the end of the line.
     Each nonempty line defines mapping for a single UID. It must
     consist of two fields separated by any amount of whitespace.  The
     first field defines original username and UID. It can be a valid
     user name or a valid UID prefixed with a plus sign.  In both cases
     the corresponding UID or user name is inferred from the current
     host’s user database.

     The second field defines the UID and username to map the original
     one to.  Its format can be the same as described above.  Otherwise,
     it can have the form NEWNAME:NEWUID, in which case neither NEWNAME
     nor NEWUID are required to be valid as per the user database.

     For example, consider the following file:

          +10     bin
          smith   root:0

     Given this file, each input file that is owner by UID 10 will be
     stored in archive with owner name ‘bin’ and owner UID corresponding
     to ‘bin’.  Each file owned by user ‘smith’ will be stored with
     owner name ‘root’ and owner ID 0.  Other files will remain
     unchanged.

     When used together with ‘--owner-map’, the ‘--owner’ option affects
     only files whose owner is not listed in the map file.

‘--group-map=FILE’
     Read GID translation map from FILE.

     The format of FILE is the same as for ‘--owner-map’ option:

     Each nonempty line defines mapping for a single GID. It must
     consist of two fields separated by any amount of whitespace.  The
     first field defines original group name and GID. It can be a valid
     group name or a valid GID prefixed with a plus sign.  In both cases
     the corresponding GID or user name is inferred from the current
     host’s group database.

     The second field defines the GID and group name to map the original
     one to.  Its format can be the same as described above.  Otherwise,
     it can have the form NEWNAME:NEWGID, in which case neither NEWNAME
     nor NEWGID are required to be valid as per the group database.

     When used together with ‘--group-map’, the ‘--group’ option affects
     only files whose owner group is not rewritten using the map file.


File: tar.info,  Node: Extended File Attributes,  Next: Ignore Failed Read,  Prev: override,  Up: create options

4.3.2 Extended File Attributes
------------------------------

Extended file attributes are name-value pairs that can be associated
with each node in a file system.  Despite the fact that POSIX.1e draft
which proposed them has been withdrawn, the extended file attributes are
supported by many file systems.  GNU ‘tar’ can store extended file
attributes along with the files.  This feature is controlled by the
following command line arguments:

‘--xattrs’
     Enable extended attributes support.  When used with ‘--create’,
     this option instructs GNU ‘tar’ to store extended file attribute in
     the created archive.  This implies POSIX.1-2001 archive format
     (‘--format=pax’).

     When used with ‘--extract’, this option tells ‘tar’, for each file
     extracted, to read stored attributes from the archive and to apply
     them to the file.

‘--no-xattrs’
     Disable extended attributes support.  This is the default.

   Attribute names are strings prefixed by a “namespace” name and a dot.
Currently, four namespaces exist: ‘user’, ‘trusted’, ‘security’ and
‘system’.  By default, when ‘--xattrs’ is used, all names are stored in
the archive (with ‘--create’), but only ‘user’ namespace is extracted
(if using ‘--extract’).  The reason for this behavior is that any other,
system defined attributes don’t provide us sufficient compatibility
promise.  Storing all attributes is safe operation for the archiving
purposes.  Though extracting those (often security related) attributes
on a different system than originally archived can lead to extraction
failures, or even misinterpretations.  This behavior can be controlled
using the following options:

‘--xattrs-exclude=PATTERN’
     Specify exclude pattern for extended attributes.

‘--xattrs-include=PATTERN’
     Specify include pattern for extended attributes.

   Here, the PATTERN is a globbing pattern.  For example, the following
command:

     $ tar --xattrs --xattrs-exclude='user.*' -cf a.tar .

   will include in the archive ‘a.tar’ all attributes, except those from
the ‘user’ namespace.

   Users shall check the attributes are binary compatible with the
target system before any other namespace is extracted with an explicit
‘--xattrs-include’ option.

   Any number of these options can be given, thereby creating lists of
include and exclude patterns.

   When both options are used, first ‘--xattrs-include’ is applied to
select the set of attribute names to keep, and then ‘--xattrs-exclude’
is applied to the resulting set.  In other words, only those attributes
will be stored, whose names match one of the regexps in
‘--xattrs-include’ and don’t match any of the regexps from
‘--xattrs-exclude’.

   When listing the archive, if both ‘--xattrs’ and ‘--verbose’ options
are given, files that have extended attributes are marked with an
asterisk following their permission mask.  For example:

     -rw-r--r--* smith/users      110 2016-03-16 16:07 file

   When two or more ‘--verbose’ options are given, a detailed listing of
extended attributes is printed after each file entry.  Each attribute is
listed on a separate line, which begins with two spaces and the letter
‘x’ indicating extended attribute.  It is followed by a colon, length of
the attribute and its name, e.g.:

     -rw-r--r--* smith/users      110 2016-03-16 16:07 file
       x:  7 user.mime_type
       x: 32 trusted.md5sum

   File access control lists (“ACL”) are another actively used feature
proposed by the POSIX.1e standard.  Each ACL consists of a set of ACL
entries, each of which describes the access permissions on the file for
an individual user or a group of users as a combination of read, write
and search/execute permissions.

   Whether or not to use ACLs is controlled by the following two
options:

‘--acls’
     Enable POSIX ACLs support.  When used with ‘--create’, this option
     instructs GNU ‘tar’ to store ACLs in the created archive.  This
     implies POSIX.1-2001 archive format (‘--format=pax’).

     When used with ‘--extract’, this option tells ‘tar’, to restore
     ACLs for each file extracted (provided they are present in the
     archive).

‘--no-acls’
     Disable POSIX ACLs support.  This is the default.

   When listing the archive, if both ‘--acls’ and ‘--verbose’ options
are given, files that have ACLs are marked with a plus sign following
their permission mask.  For example:

     -rw-r--r--+ smith/users      110 2016-03-16 16:07 file

   When two or more ‘--verbose’ options are given, a detailed listing of
ACL is printed after each file entry:

     -rw-r--r--+ smith/users      110 2016-03-16 16:07 file
       a: user::rw-,user:gray:-w-,group::r--,mask::rw-,other::r--

   “Security-Enhanced Linux” (“SELinux” for short) is a Linux kernel
security module that provides a mechanism for supporting access control
security policies, including so-called mandatory access controls
(“MAC”). Support for SELinux attributes is controlled by the following
command line options:

‘--selinux’
     Enable the SELinux context support.

‘--no-selinux’
     Disable SELinux context support.


File: tar.info,  Node: Ignore Failed Read,  Prev: Extended File Attributes,  Up: create options

4.3.3 Ignore Failed Read
------------------------

‘--ignore-failed-read’
     Do not exit with nonzero if there are mild problems while reading.

   This option has effect only during creation.  It instructs tar to
treat as mild conditions any missing or unreadable files (directories),
or files that change while reading.  Such failures don’t affect the
program exit code, and the corresponding diagnostic messages are marked
as warnings, not errors.  These warnings can be suppressed using the
‘--warning=failed-read’ option (*note warnings::).


File: tar.info,  Node: extract options,  Next: backup,  Prev: create options,  Up: operations

4.4 Options Used by ‘--extract’
===============================

The previous chapter showed how to use ‘--extract’ to extract an archive
into the file system.  Various options cause ‘tar’ to extract more
information than just file contents, such as the owner, the permissions,
the modification date, and so forth.  This section presents options to
be used with ‘--extract’ when certain special considerations arise.  You
may review the information presented in *note extract:: for more basic
information about the ‘--extract’ operation.

* Menu:

* Reading::                     Options to Help Read Archives
* Writing::                     Changing How ‘tar’ Writes Files
* Scarce::                      Coping with Scarce Resources


File: tar.info,  Node: Reading,  Next: Writing,  Up: extract options

4.4.1 Options to Help Read Archives
-----------------------------------

Normally, ‘tar’ will request data in full record increments from an
archive storage device.  If the device cannot return a full record,
‘tar’ will report an error.  However, some devices do not always return
full records, or do not require the last record of an archive to be
padded out to the next record boundary.  To keep reading until you
obtain a full record, or to accept an incomplete record if it contains
an end-of-archive marker, specify the ‘--read-full-records’ (‘-B’)
option in conjunction with the ‘--extract’ or ‘--list’ operations.
*Note Blocking::.

   The ‘--read-full-records’ (‘-B’) option is turned on by default when
‘tar’ reads an archive from standard input, or from a remote machine.
This is because on BSD Unix systems, attempting to read a pipe returns
however much happens to be in the pipe, even if it is less than was
requested.  If this option were not enabled, ‘tar’ would fail as soon as
it read an incomplete record from the pipe.

   If you’re not sure of the blocking factor of an archive, you can read
the archive by specifying ‘--read-full-records’ (‘-B’) and
‘--blocking-factor=512-SIZE’ (‘-b 512-SIZE’), using a blocking factor
larger than what the archive uses.  This lets you avoid having to
determine the blocking factor of an archive.  *Note Blocking Factor::.

* Menu:

* read full records::
* Ignore Zeros::


File: tar.info,  Node: read full records,  Next: Ignore Zeros,  Up: Reading

Reading Full Records
....................

‘--read-full-records’
‘-B’
     Use in conjunction with ‘--extract’ (‘--get’, ‘-x’) to read an
     archive which contains incomplete records, or one which has a
     blocking factor less than the one specified.


File: tar.info,  Node: Ignore Zeros,  Prev: read full records,  Up: Reading

Ignoring Blocks of Zeros
........................

Normally, ‘tar’ stops reading when it encounters a block of zeros
between file entries (which usually indicates the end of the archive).
‘--ignore-zeros’ (‘-i’) allows ‘tar’ to completely read an archive which
contains a block of zeros before the end (i.e., a damaged archive, or
one that was created by concatenating several archives together).  This
option also suppresses warnings about missing or incomplete zero blocks
at the end of the archive.  This can be turned on, if the need be, using
the ‘--warning=alone-zero-block --warning=missing-zero-blocks’ options
(*note warnings::).

   The ‘--ignore-zeros’ (‘-i’) option is turned off by default because
many versions of ‘tar’ write garbage after the end-of-archive entry,
since that part of the media is never supposed to be read.  GNU ‘tar’
does not write after the end of an archive, but seeks to maintain
compatibility among archiving utilities.

‘--ignore-zeros’
‘-i’
     To ignore blocks of zeros (i.e., end-of-archive entries) which may
     be encountered while reading an archive.  Use in conjunction with
     ‘--extract’ or ‘--list’.


File: tar.info,  Node: Writing,  Next: Scarce,  Prev: Reading,  Up: extract options

4.4.2 Changing How ‘tar’ Writes Files
-------------------------------------

     _(This message will disappear, once this node revised.)_

* Menu:

* Dealing with Old Files::
* Overwrite Old Files::
* Keep Old Files::
* Keep Newer Files::
* Unlink First::
* Recursive Unlink::
* Data Modification Times::
* Setting Access Permissions::
* Directory Modification Times and Permissions::
* Writing to Standard Output::
* Writing to an External Program::
* remove files::


File: tar.info,  Node: Dealing with Old Files,  Next: Overwrite Old Files,  Up: Writing

Options Controlling the Overwriting of Existing Files
.....................................................

When extracting files, if ‘tar’ discovers that the extracted file
already exists, it normally replaces the file by removing it before
extracting it, to prevent confusion in the presence of hard or symbolic
links.  (If the existing file is a symbolic link, it is removed, not
followed.)  However, if a directory cannot be removed because it is
nonempty, ‘tar’ normally overwrites its metadata (ownership, permission,
etc.).  The ‘--overwrite-dir’ option enables this default behavior.  To
be more cautious and preserve the metadata of such a directory, use the
‘--no-overwrite-dir’ option.

   To be even more cautious and prevent existing files from being
replaced, use the ‘--keep-old-files’ (‘-k’) option.  It causes ‘tar’ to
refuse to replace or update a file that already exists, i.e., a file
with the same name as an archive member prevents extraction of that
archive member.  Instead, it reports an error.  For example:

     $ ls
     blues
     $ tar -x -k -f archive.tar
     tar: blues: Cannot open: File exists
     tar: Exiting with failure status due to previous errors

   If you wish to preserve old files untouched, but don’t want ‘tar’ to
treat them as errors, use the ‘--skip-old-files’ option.  This option
causes ‘tar’ to silently skip extracting over existing files.

   To be more aggressive about altering existing files, use the
‘--overwrite’ option.  It causes ‘tar’ to overwrite existing files and
to follow existing symbolic links when extracting.

   Some people argue that GNU ‘tar’ should not hesitate to overwrite
files with other files when extracting.  When extracting a ‘tar’
archive, they expect to see a faithful copy of the state of the file
system when the archive was created.  It is debatable that this would
always be a proper behavior.  For example, suppose one has an archive in
which ‘usr/local’ is a link to ‘usr/local2’.  Since then, maybe the site
removed the link and renamed the whole hierarchy from ‘/usr/local2’ to
‘/usr/local’.  Such things happen all the time.  I guess it would not be
welcome at all that GNU ‘tar’ removes the whole hierarchy just to make
room for the link to be reinstated (unless it _also_ simultaneously
restores the full ‘/usr/local2’, of course!)  GNU ‘tar’ is indeed able
to remove a whole hierarchy to reestablish a symbolic link, for example,
but _only if_ ‘--recursive-unlink’ is specified to allow this behavior.
In any case, single files are silently removed.

   Finally, the ‘--unlink-first’ (‘-U’) option can improve performance
in some cases by causing ‘tar’ to remove files unconditionally before
extracting them.


File: tar.info,  Node: Overwrite Old Files,  Next: Keep Old Files,  Prev: Dealing with Old Files,  Up: Writing

Overwrite Old Files
...................

‘--overwrite’
     Overwrite existing files and directory metadata when extracting
     files from an archive.

     This causes ‘tar’ to write extracted files into the file system
     without regard to the files already on the system; i.e., files with
     the same names as archive members are overwritten when the archive
     is extracted.  It also causes ‘tar’ to extract the ownership,
     permissions, and time stamps onto any preexisting files or
     directories.  If the name of a corresponding file name is a
     symbolic link, the file pointed to by the symbolic link will be
     overwritten instead of the symbolic link itself (if this is
     possible).  Moreover, special devices, empty directories and even
     symbolic links are automatically removed if they are in the way of
     extraction.

     Be careful when using the ‘--overwrite’ option, particularly when
     combined with the ‘--absolute-names’ (‘-P’) option, as this
     combination can change the contents, ownership or permissions of
     any file on your system.  Also, many systems do not take kindly to
     overwriting files that are currently being executed.

‘--overwrite-dir’
     Overwrite the metadata of directories when extracting files from an
     archive, but remove other files before extracting.


File: tar.info,  Node: Keep Old Files,  Next: Keep Newer Files,  Prev: Overwrite Old Files,  Up: Writing

Keep Old Files
..............

GNU ‘tar’ provides two options to control its actions in a situation
when it is about to extract a file which already exists on disk.

‘--keep-old-files’
‘-k’
     Do not replace existing files from archive.  When such a file is
     encountered, ‘tar’ issues an error message.  Upon end of
     extraction, ‘tar’ exits with code 2 (*note exit status::).

‘--skip-old-files’
     Do not replace existing files from archive, but do not treat that
     as error.  Such files are silently skipped and do not affect ‘tar’
     exit status.

     Additional verbosity can be obtained using
     ‘--warning=existing-file’ together with that option (*note
     warnings::).


File: tar.info,  Node: Keep Newer Files,  Next: Unlink First,  Prev: Keep Old Files,  Up: Writing

Keep Newer Files
................

‘--keep-newer-files’
     Do not replace existing files that are newer than their archive
     copies.  This option is meaningless with ‘--list’ (‘-t’).


File: tar.info,  Node: Unlink First,  Next: Recursive Unlink,  Prev: Keep Newer Files,  Up: Writing

Unlink First
............

‘--unlink-first’
‘-U’
     Remove files before extracting over them.  This can make ‘tar’ run
     a bit faster if you know in advance that the extracted files all
     need to be removed.  Normally this option slows ‘tar’ down
     slightly, so it is disabled by default.


File: tar.info,  Node: Recursive Unlink,  Next: Data Modification Times,  Prev: Unlink First,  Up: Writing

Recursive Unlink
................

‘--recursive-unlink’
     When this option is specified, try removing files and directory
     hierarchies before extracting over them.  _This is a dangerous
     option!_

   If you specify the ‘--recursive-unlink’ option, ‘tar’ removes
_anything_ that keeps you from extracting a file as far as current
permissions will allow it.  This could include removal of the contents
of a full directory hierarchy.


File: tar.info,  Node: Data Modification Times,  Next: Setting Access Permissions,  Prev: Recursive Unlink,  Up: Writing

Setting Data Modification Times
...............................

Normally, ‘tar’ sets the data modification times of extracted files to
the corresponding times recorded for the files in the archive, but
limits the permissions of extracted files by the current ‘umask’
setting.

   To set the data modification times of extracted files to the time
when the files were extracted, use the ‘--touch’ (‘-m’) option in
conjunction with ‘--extract’ (‘--get’, ‘-x’).

‘--touch’
‘-m’
     Sets the data modification time of extracted archive members to the
     time they were extracted, not the time recorded for them in the
     archive.  Use in conjunction with ‘--extract’ (‘--get’, ‘-x’).


File: tar.info,  Node: Setting Access Permissions,  Next: Directory Modification Times and Permissions,  Prev: Data Modification Times,  Up: Writing

Setting Access Permissions
..........................

To set the modes (access permissions) of extracted files to those
recorded for those files in the archive, use ‘--same-permissions’ in
conjunction with the ‘--extract’ (‘--get’, ‘-x’) operation.

‘--preserve-permissions’
‘--same-permissions’
‘-p’
     Set modes of extracted archive members to those recorded in the
     archive, instead of current umask settings.  Use in conjunction
     with ‘--extract’ (‘--get’, ‘-x’).


File: tar.info,  Node: Directory Modification Times and Permissions,  Next: Writing to Standard Output,  Prev: Setting Access Permissions,  Up: Writing

Directory Modification Times and Permissions
............................................

After successfully extracting a file member, GNU ‘tar’ normally restores
its permissions and modification times, as described in the previous
sections.  This cannot be done for directories, because after extracting
a directory ‘tar’ will almost certainly extract files into that
directory and this will cause the directory modification time to be
updated.  Moreover, restoring that directory permissions may not permit
file creation within it.  Thus, restoring directory permissions and
modification times must be delayed at least until all files have been
extracted into that directory.  GNU ‘tar’ restores directories using the
following approach.

   The extracted directories are created with the mode specified in the
archive, as modified by the umask of the user, which gives sufficient
permissions to allow file creation.  The meta-information about the
directory is recorded in the temporary list of directories.  When
preparing to extract next archive member, GNU ‘tar’ checks if the
directory prefix of this file contains the remembered directory.  If it
does not, the program assumes that all files have been extracted into
that directory, restores its modification time and permissions and
removes its entry from the internal list.  This approach allows to
correctly restore directory meta-information in the majority of cases,
while keeping memory requirements sufficiently small.  It is based on
the fact, that most ‘tar’ archives use the predefined order of members:
first the directory, then all the files and subdirectories in that
directory.

   However, this is not always true.  The most important exception are
incremental archives (*note Incremental Dumps::).  The member order in
an incremental archive is reversed: first all directory members are
stored, followed by other (non-directory) members.  So, when extracting
from incremental archives, GNU ‘tar’ alters the above procedure.  It
remembers all restored directories, and restores their meta-data only
after the entire archive has been processed.  Notice, that you do not
need to specify any special options for that, as GNU ‘tar’ automatically
detects archives in incremental format.

   There may be cases, when such processing is required for normal
archives too.  Consider the following example:

     $ tar --no-recursion -cvf archive \
         foo foo/file1 bar bar/file foo/file2
     foo/
     foo/file1
     bar/
     bar/file
     foo/file2

   During the normal operation, after encountering ‘bar’ GNU ‘tar’ will
assume that all files from the directory ‘foo’ were already extracted
and will therefore restore its timestamp and permission bits.  However,
after extracting ‘foo/file2’ the directory timestamp will be offset
again.

   To correctly restore directory meta-information in such cases, use
the ‘--delay-directory-restore’ command line option:

‘--delay-directory-restore’
     Delays restoring of the modification times and permissions of
     extracted directories until the end of extraction.  This way,
     correct meta-information is restored even if the archive has
     unusual member ordering.

‘--no-delay-directory-restore’
     Cancel the effect of the previous ‘--delay-directory-restore’.  Use
     this option if you have used ‘--delay-directory-restore’ in
     ‘TAR_OPTIONS’ variable (*note TAR_OPTIONS::) and wish to
     temporarily disable it.


File: tar.info,  Node: Writing to Standard Output,  Next: Writing to an External Program,  Prev: Directory Modification Times and Permissions,  Up: Writing

Writing to Standard Output
..........................

To write the extracted files to the standard output, instead of creating
the files on the file system, use ‘--to-stdout’ (‘-O’) in conjunction
with ‘--extract’ (‘--get’, ‘-x’).  This option is useful if you are
extracting files to send them through a pipe, and do not need to
preserve them in the file system.  If you extract multiple members, they
appear on standard output concatenated, in the order they are found in
the archive.

‘--to-stdout’
‘-O’
     Writes files to the standard output.  Use only in conjunction with
     ‘--extract’ (‘--get’, ‘-x’).  When this option is used, instead of
     creating the files specified, ‘tar’ writes the contents of the
     files extracted to its standard output.  This may be useful if you
     are only extracting the files in order to send them through a pipe.
     This option is meaningless with ‘--list’ (‘-t’).

   This can be useful, for example, if you have a tar archive containing
a big file and don’t want to store the file on disk before processing
it.  You can use a command like this:

     tar -xOzf foo.tgz bigfile | process

   or even like this if you want to process the concatenation of the
files:

     tar -xOzf foo.tgz bigfile1 bigfile2 | process

   However, ‘--to-command’ may be more convenient for use with multiple
files.  See the next section.


File: tar.info,  Node: Writing to an External Program,  Next: remove files,  Prev: Writing to Standard Output,  Up: Writing

Writing to an External Program
..............................

You can instruct ‘tar’ to send the contents of each extracted file to
the standard input of an external program:

‘--to-command=COMMAND’
     Extract files and pipe their contents to the standard input of
     COMMAND.  When this option is used, instead of creating the files
     specified, ‘tar’ invokes COMMAND and pipes the contents of the
     files to its standard output.  The COMMAND may contain command line
     arguments (see *note Running External Commands: external, for more
     detail).

     Notice, that COMMAND is executed once for each regular file
     extracted.  Non-regular files (directories, etc.) are ignored when
     this option is used.

   The command can obtain the information about the file it processes
from the following environment variables:

‘TAR_FILETYPE’
     Type of the file.  It is a single letter with the following
     meaning:

     f       Regular file
     d       Directory
     l       Symbolic link
     h       Hard link
     b       Block device
     c       Character device

     Currently only regular files are supported.

‘TAR_MODE’
     File mode, an octal number.

‘TAR_FILENAME’
     The name of the file.

‘TAR_REALNAME’
     Name of the file as stored in the archive.

‘TAR_UNAME’
     Name of the file owner.

‘TAR_GNAME’
     Name of the file owner group.

‘TAR_ATIME’
     Time of last access.  It is a decimal number, representing seconds
     since the Epoch.  If the archive provides times with nanosecond
     precision, the nanoseconds are appended to the timestamp after a
     decimal point.

‘TAR_MTIME’
     Time of last modification.

‘TAR_CTIME’
     Time of last status change.

‘TAR_SIZE’
     Size of the file.

‘TAR_UID’
     UID of the file owner.

‘TAR_GID’
     GID of the file owner.

   Additionally, the following variables contain information about tar
mode and the archive being processed:

‘TAR_VERSION’
     GNU ‘tar’ version number.

‘TAR_ARCHIVE’
     The name of the archive ‘tar’ is processing.

‘TAR_BLOCKING_FACTOR’
     Current blocking factor (*note Blocking::).

‘TAR_VOLUME’
     Ordinal number of the volume ‘tar’ is processing.

‘TAR_FORMAT’
     Format of the archive being processed.  *Note Formats::, for a
     complete list of archive format names.

   These variables are defined prior to executing the command, so you
can pass them as arguments, if you prefer.  For example, if the command
PROC takes the member name and size as its arguments, then you could do:

     $ tar -x -f archive.tar \
            --to-command='proc $TAR_FILENAME $TAR_SIZE'

Notice single quotes to prevent variable names from being expanded by
the shell when invoking ‘tar’.

   If COMMAND exits with a non-0 status, ‘tar’ will print an error
message similar to the following:

     tar: 2345: Child returned status 1

   Here, ‘2345’ is the PID of the finished process.

   If this behavior is not wanted, use ‘--ignore-command-error’:

‘--ignore-command-error’
     Ignore exit codes of subprocesses.  Notice that if the program
     exits on signal or otherwise terminates abnormally, the error
     message will be printed even if this option is used.

‘--no-ignore-command-error’
     Cancel the effect of any previous ‘--ignore-command-error’ option.
     This option is useful if you have set ‘--ignore-command-error’ in
     ‘TAR_OPTIONS’ (*note TAR_OPTIONS::) and wish to temporarily cancel
     it.


File: tar.info,  Node: remove files,  Prev: Writing to an External Program,  Up: Writing

Removing Files
..............

‘--remove-files’
     Remove files after adding them to the archive.


File: tar.info,  Node: Scarce,  Prev: Writing,  Up: extract options

4.4.3 Coping with Scarce Resources
----------------------------------

     _(This message will disappear, once this node revised.)_

* Menu:

* Starting File::
* Same Order::


File: tar.info,  Node: Starting File,  Next: Same Order,  Up: Scarce

Starting File
.............

‘--starting-file=NAME’
‘-K NAME’
     Starts an operation in the middle of an archive.  Use in
     conjunction with ‘--extract’ (‘--get’, ‘-x’) or ‘--list’ (‘-t’).

   If a previous attempt to extract files failed due to lack of disk
space, you can use ‘--starting-file=NAME’ (‘-K NAME’) to start
extracting only after member NAME of the archive.  This assumes, of
course, that there is now free space, or that you are now extracting
into a different file system.  (You could also choose to suspend ‘tar’,
remove unnecessary files from the file system, and then resume the same
‘tar’ operation.  In this case, ‘--starting-file’ is not necessary.)
See also *note interactive::, and *note exclude::.


File: tar.info,  Node: Same Order,  Prev: Starting File,  Up: Scarce

Same Order
..........

‘--same-order’
‘--preserve-order’
‘-s’
     To process large lists of file names on machines with small amounts
     of memory.  Use in conjunction with ‘--compare’ (‘--diff’, ‘-d’),
     ‘--list’ (‘-t’) or ‘--extract’ (‘--get’, ‘-x’).

   The ‘--same-order’ (‘--preserve-order’, ‘-s’) option tells ‘tar’ that
the list of file names to be listed or extracted is sorted in the same
order as the files in the archive.  This allows a large list of names to
be used, even on a small machine that would not otherwise be able to
hold all the names in memory at the same time.  Such a sorted list can
easily be created by running ‘tar -t’ on the archive and editing its
output.

   This option is probably never needed on modern computer systems.


File: tar.info,  Node: backup,  Next: looking ahead,  Prev: extract options,  Up: operations

4.5 Backup options
==================

GNU ‘tar’ offers options for making backups of files before writing new
versions.  These options control the details of these backups.  They may
apply to the archive itself before it is created or rewritten, as well
as individual extracted members.  Other GNU programs (‘cp’, ‘install’,
‘ln’, and ‘mv’, for example) offer similar options.

   Backup options may prove unexpectedly useful when extracting archives
containing many members having identical name, or when extracting
archives on systems having file name limitations, making different
members appear as having similar names through the side-effect of name
truncation.

   When any existing file is backed up before being overwritten by
extraction, then clashing files are automatically be renamed to be
unique, and the true name is kept for only the last file of a series of
clashing files.  By using verbose mode, users may track exactly what
happens.

   At the detail level, some decisions are still experimental, and may
change in the future, we are waiting comments from our users.  So,
please do not learn to depend blindly on the details of the backup
features.  For example, currently, directories themselves are never
renamed through using these options, so, extracting a file over a
directory still has good chances to fail.  Also, backup options apply to
created archives, not only to extracted members.  For created archives,
backups will not be attempted when the archive is a block or character
device, or when it refers to a remote file.

   For the sake of simplicity and efficiency, backups are made by
renaming old files prior to creation or extraction, and not by copying.
The original name is restored if the file creation fails.  If a failure
occurs after a partial extraction of a file, both the backup and the
partially extracted file are kept.

‘--backup[=METHOD]’
     Back up files that are about to be overwritten or removed.  Without
     this option, the original versions are destroyed.

     Use METHOD to determine the type of backups made.  If METHOD is not
     specified, use the value of the ‘VERSION_CONTROL’ environment
     variable.  And if ‘VERSION_CONTROL’ is not set, use the ‘existing’
     method.

     This option corresponds to the Emacs variable ‘version-control’;
     the same values for METHOD are accepted as in Emacs.  This option
     also allows more descriptive names.  The valid METHODs are:

     ‘t’
     ‘numbered’
          Always make numbered backups.

     ‘nil’
     ‘existing’
          Make numbered backups of files that already have them, simple
          backups of the others.

     ‘never’
     ‘simple’
          Always make simple backups.

‘--suffix=SUFFIX’
     Append SUFFIX to each backup file made with ‘--backup’.  If this
     option is not specified, the value of the ‘SIMPLE_BACKUP_SUFFIX’
     environment variable is used.  And if ‘SIMPLE_BACKUP_SUFFIX’ is not
     set, the default is ‘~’, just as in Emacs.


File: tar.info,  Node: looking ahead,  Prev: backup,  Up: operations

4.6 Looking Ahead: The Rest of this Manual
==========================================

You have now seen how to use all eight of the operations available to
‘tar’, and a number of the possible options.  The next chapter explains
how to choose and change file and archive names, how to use files to
store names of other files which you can then call as arguments to ‘tar’
(this can help you save time if you expect to archive the same list of
files a number of times), and so forth.

   If there are too many files to conveniently list on the command line,
you can list the names in a file, and ‘tar’ will read that file.  *Note
files::.

   There are various ways of causing ‘tar’ to skip over some files, and
not archive them.  *Note Choosing::.


File: tar.info,  Node: Backups,  Next: Choosing,  Prev: operations,  Up: Top

5 Performing Backups and Restoring Files
****************************************

GNU ‘tar’ is distributed along with the scripts for performing backups
and restores.  Even if there is a good chance those scripts may be
satisfying to you, they are not the only scripts or methods available
for doing backups and restore.  You may well create your own, or use
more sophisticated packages dedicated to that purpose.

   Some users are enthusiastic about ‘Amanda’ (The Advanced Maryland
Automatic Network Disk Archiver), a backup system developed by James da
Silva ‘jds@cs.umd.edu’ and available on many Unix systems.  This is free
software, and it is available from <http://www.amanda.org>.

   This chapter documents both the provided shell scripts and ‘tar’
options which are more specific to usage as a backup tool.

   To “back up” a file system means to create archives that contain all
the files in that file system.  Those archives can then be used to
restore any or all of those files (for instance if a disk crashes or a
file is accidentally deleted).  File system “backups” are also called
“dumps”.

* Menu:

* Full Dumps::                  Using ‘tar’ to Perform Full Dumps
* Incremental Dumps::           Using ‘tar’ to Perform Incremental Dumps
* Backup Levels::               Levels of Backups
* Backup Parameters::           Setting Parameters for Backups and Restoration
* Scripted Backups::            Using the Backup Scripts
* Scripted Restoration::        Using the Restore Script


File: tar.info,  Node: Full Dumps,  Next: Incremental Dumps,  Up: Backups

5.1 Using ‘tar’ to Perform Full Dumps
=====================================

     _(This message will disappear, once this node revised.)_

   Full dumps should only be made when no other people or programs are
modifying files in the file system.  If files are modified while ‘tar’
is making the backup, they may not be stored properly in the archive, in
which case you won’t be able to restore them if you have to.  (Files not
being modified are written with no trouble, and do not corrupt the
entire archive.)

   You will want to use the ‘--label=ARCHIVE-LABEL’ (‘-V ARCHIVE-LABEL’)
option to give the archive a volume label, so you can tell what this
archive is even if the label falls off the tape, or anything like that.

   Unless the file system you are dumping is guaranteed to fit on one
volume, you will need to use the ‘--multi-volume’ (‘-M’) option.  Make
sure you have enough tapes on hand to complete the backup.

   If you want to dump each file system separately you will need to use
the ‘--one-file-system’ option to prevent ‘tar’ from crossing file
system boundaries when storing (sub)directories.

   The ‘--incremental’ (‘-G’) (*note Incremental Dumps::) option is not
needed, since this is a complete copy of everything in the file system,
and a full restore from this backup would only be done onto a completely
empty disk.

   Unless you are in a hurry, and trust the ‘tar’ program (and your
tapes), it is a good idea to use the ‘--verify’ (‘-W’) option, to make
sure your files really made it onto the dump properly.  This will also
detect cases where the file was modified while (or just after) it was
being archived.  Not all media (notably cartridge tapes) are capable of
being verified, unfortunately.


File: tar.info,  Node: Incremental Dumps,  Next: Backup Levels,  Prev: Full Dumps,  Up: Backups

5.2 Using ‘tar’ to Perform Incremental Dumps
============================================

“Incremental backup” is a special form of GNU ‘tar’ archive that stores
additional metadata so that exact state of the file system can be
restored when extracting the archive.

   GNU ‘tar’ currently offers two options for handling incremental
backups: ‘--listed-incremental=SNAPSHOT-FILE’ (‘-g SNAPSHOT-FILE’) and
‘--incremental’ (‘-G’).

   The option ‘--listed-incremental’ instructs tar to operate on an
incremental archive with additional metadata stored in a standalone
file, called a “snapshot file”.  The purpose of this file is to help
determine which files have been changed, added or deleted since the last
backup, so that the next incremental backup will contain only modified
files.  The name of the snapshot file is given as an argument to the
option:

‘--listed-incremental=FILE’
‘-g FILE’
     Handle incremental backups with snapshot data in FILE.

   To create an incremental backup, you would use ‘--listed-incremental’
together with ‘--create’ (*note create::).  For example:

     $ tar --create \
                --file=archive.1.tar \
                --listed-incremental=/var/log/usr.snar \
                /usr

   This will create in ‘archive.1.tar’ an incremental backup of the
‘/usr’ file system, storing additional metadata in the file
‘/var/log/usr.snar’.  If this file does not exist, it will be created.
The created archive will then be a “level 0 backup”; please see the next
section for more on backup levels.

   Otherwise, if the file ‘/var/log/usr.snar’ exists, it determines
which files are modified.  In this case only these files will be stored
in the archive.  Suppose, for example, that after running the above
command, you delete file ‘/usr/doc/old’ and create directory
‘/usr/local/db’ with the following contents:

     $ ls /usr/local/db
     /usr/local/db/data
     /usr/local/db/index

   Some time later you create another incremental backup.  You will then
see:

     $ tar --create \
                --file=archive.2.tar \
                --listed-incremental=/var/log/usr.snar \
                /usr
     tar: usr/local/db: Directory is new
     usr/local/db/
     usr/local/db/data
     usr/local/db/index

The created archive ‘archive.2.tar’ will contain only these three
members.  This archive is called a “level 1 backup”.  Notice that
‘/var/log/usr.snar’ will be updated with the new data, so if you plan to
create more ‘level 1’ backups, it is necessary to create a working copy
of the snapshot file before running ‘tar’.  The above example will then
be modified as follows:

     $ cp /var/log/usr.snar /var/log/usr.snar-1
     $ tar --create \
                --file=archive.2.tar \
                --listed-incremental=/var/log/usr.snar-1 \
                /usr

   You can force ‘level 0’ backups either by removing the snapshot file
before running ‘tar’, or by supplying the ‘--level=0’ option, e.g.:

     $ tar --create \
                --file=archive.2.tar \
                --listed-incremental=/var/log/usr.snar-0 \
                --level=0 \
                /usr

   Incremental dumps depend crucially on time stamps, so the results are
unreliable if you modify a file’s time stamps during dumping (e.g., with
the ‘--atime-preserve=replace’ option), or if you set the clock
backwards.

   Metadata stored in snapshot files include device numbers, which,
obviously are supposed to be non-volatile values.  However, it turns out
that NFS devices have undependable values when an automounter gets in
the picture.  This can lead to a great deal of spurious redumping in
incremental dumps, so it is somewhat useless to compare two NFS devices
numbers over time.  The solution implemented currently is to consider
all NFS devices as being equal when it comes to comparing directories;
this is fairly gross, but there does not seem to be a better way to go.

   Apart from using NFS, there are a number of cases where relying on
device numbers can cause spurious redumping of unmodified files.  For
example, this occurs when archiving LVM snapshot volumes.  To avoid
this, use ‘--no-check-device’ option:

‘--no-check-device’
     Do not rely on device numbers when preparing a list of changed
     files for an incremental dump.

‘--check-device’
     Use device numbers when preparing a list of changed files for an
     incremental dump.  This is the default behavior.  The purpose of
     this option is to undo the effect of the ‘--no-check-device’ if it
     was given in ‘TAR_OPTIONS’ environment variable (*note
     TAR_OPTIONS::).

   There is also another way to cope with changing device numbers.  It
is described in detail in *note Fixing Snapshot Files::.

   Note that incremental archives use ‘tar’ extensions and may not be
readable by non-GNU versions of the ‘tar’ program.

   To extract from the incremental dumps, use ‘--listed-incremental’
together with ‘--extract’ option (*note extracting files::).  In this
case, ‘tar’ does not need to access snapshot file, since all the data
necessary for extraction are stored in the archive itself.  So, when
extracting, you can give whatever argument to ‘--listed-incremental’,
the usual practice is to use ‘--listed-incremental=/dev/null’.
Alternatively, you can use ‘--incremental’, which needs no arguments.
In general, ‘--incremental’ (‘-G’) can be used as a shortcut for
‘--listed-incremental’ when listing or extracting incremental backups
(for more information regarding this option, *note incremental-op::).

   When extracting from the incremental backup GNU ‘tar’ attempts to
restore the exact state the file system had when the archive was
created.  In particular, it will _delete_ those files in the file system
that did not exist in their directories when the archive was created.
If you have created several levels of incremental files, then in order
to restore the exact contents the file system had when the last level
was created, you will need to restore from all backups in turn.
Continuing our example, to restore the state of ‘/usr’ file system, one
would do(1):

     $ tar --extract \
                --listed-incremental=/dev/null \
                --file archive.1.tar
     $ tar --extract \
                --listed-incremental=/dev/null \
                --file archive.2.tar

   To list the contents of an incremental archive, use ‘--list’ (*note
list::), as usual.  To obtain more information about the archive, use
‘--listed-incremental’ or ‘--incremental’ combined with two ‘--verbose’
options(2):

     tar --list --incremental --verbose --verbose --file archive.tar

   This command will print, for each directory in the archive, the list
of files in that directory at the time the archive was created.  This
information is put out in a format which is both human-readable and
unambiguous for a program: each file name is printed as

     X FILE

where X is a letter describing the status of the file: ‘Y’ if the file
is present in the archive, ‘N’ if the file is not included in the
archive, or a ‘D’ if the file is a directory (and is included in the
archive).  *Note Dumpdir::, for the detailed description of dumpdirs and
status codes.  Each such line is terminated by a newline character.  The
last line is followed by an additional newline to indicate the end of
the data.

   The option ‘--incremental’ (‘-G’) gives the same behavior as
‘--listed-incremental’ when used with ‘--list’ and ‘--extract’ options.
When used with ‘--create’ option, it creates an incremental archive
without creating snapshot file.  Thus, it is impossible to create
several levels of incremental backups with ‘--incremental’ option.

   ---------- Footnotes ----------

   (1) Notice, that since both archives were created without ‘-P’ option
(*note absolute::), these commands should be run from the root file
system.

   (2) Two ‘--verbose’ options were selected to avoid breaking usual
verbose listing output (‘--list --verbose’) when using in scripts.

   Versions of GNU ‘tar’ up to 1.15.1 used to dump verbatim binary
contents of the DUMPDIR header (with terminating nulls) when
‘--incremental’ or ‘--listed-incremental’ option was given, no matter
what the verbosity level.  This behavior, and, especially, the binary
output it produced were considered inconvenient and were changed in
version 1.16.


File: tar.info,  Node: Backup Levels,  Next: Backup Parameters,  Prev: Incremental Dumps,  Up: Backups

5.3 Levels of Backups
=====================

An archive containing all the files in the file system is called a “full
backup” or “full dump”.  You could insure your data by creating a full
dump every day.  This strategy, however, would waste a substantial
amount of archive media and user time, as unchanged files are daily
re-archived.

   It is more efficient to do a full dump only occasionally.  To back up
files between full dumps, you can use “incremental dumps”.  A “level
one” dump archives all the files that have changed since the last full
dump.

   A typical dump strategy would be to perform a full dump once a week,
and a level one dump once a day.  This means some versions of files will
in fact be archived more than once, but this dump strategy makes it
possible to restore a file system to within one day of accuracy by only
extracting two archives—the last weekly (full) dump and the last daily
(level one) dump.  The only information lost would be in files changed
or created since the last daily backup.  (Doing dumps more than once a
day is usually not worth the trouble.)

   GNU ‘tar’ comes with scripts you can use to do full and level-one
(actually, even level-two and so on) dumps.  Using scripts (shell
programs) to perform backups and restoration is a convenient and
reliable alternative to typing out file name lists and ‘tar’ commands by
hand.

   Before you use these scripts, you need to edit the file
‘backup-specs’, which specifies parameters used by the backup scripts
and by the restore script.  This file is usually located in
‘/etc/backup’ directory.  *Note Backup Parameters::, for its detailed
description.  Once the backup parameters are set, you can perform
backups or restoration by running the appropriate script.

   The name of the backup script is ‘backup’.  The name of the restore
script is ‘restore’.  The following sections describe their use in
detail.

   _Please Note:_ The backup and restoration scripts are designed to be
used together.  While it is possible to restore files by hand from an
archive which was created using a backup script, and to create an
archive by hand which could then be extracted using the restore script,
it is easier to use the scripts.  *Note Incremental Dumps::, before
making such an attempt.


File: tar.info,  Node: Backup Parameters,  Next: Scripted Backups,  Prev: Backup Levels,  Up: Backups

5.4 Setting Parameters for Backups and Restoration
==================================================

The file ‘backup-specs’ specifies backup parameters for the backup and
restoration scripts provided with ‘tar’.  You must edit ‘backup-specs’
to fit your system configuration and schedule before using these
scripts.

   Syntactically, ‘backup-specs’ is a shell script, containing mainly
variable assignments.  However, any valid shell construct is allowed in
this file.  Particularly, you may wish to define functions within that
script (e.g., see ‘RESTORE_BEGIN’ below).  For more information about
shell script syntax, please refer to the definition of the Shell Command
Language
(https://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html).
See also *note Bash Features: (bashref)Top.

   The shell variables controlling behavior of ‘backup’ and ‘restore’
are described in the following subsections.

* Menu:

* General-Purpose Variables::
* Magnetic Tape Control::
* User Hooks::
* backup-specs example::        An Example Text of ‘Backup-specs’


File: tar.info,  Node: General-Purpose Variables,  Next: Magnetic Tape Control,  Up: Backup Parameters

5.4.1 General-Purpose Variables
-------------------------------

 -- Backup variable: ADMINISTRATOR
     The user name of the backup administrator.  ‘Backup’ scripts sends
     a backup report to this address.

 -- Backup variable: BACKUP_HOUR
     The hour at which the backups are done.  This can be a number from
     0 to 23, or the time specification in form HOURS:MINUTES, or the
     string ‘now’.

     This variable is used by ‘backup’.  Its value may be overridden
     using ‘--time’ option (*note Scripted Backups::).

 -- Backup variable: TAPE_FILE

     The device ‘tar’ writes the archive to.  If TAPE_FILE is a remote
     archive (*note remote-dev::), backup script will suppose that your
     ‘mt’ is able to access remote devices.  If RSH (*note RSH::) is
     set, ‘--rsh-command’ option will be added to invocations of ‘mt’.

 -- Backup variable: BLOCKING

     The blocking factor ‘tar’ will use when writing the dump archive.
     *Note Blocking Factor::.

 -- Backup variable: BACKUP_DIRS

     A list of file systems to be dumped (for ‘backup’), or restored
     (for ‘restore’).  You can include any directory name in the list —
     subdirectories on that file system will be included, regardless of
     how they may look to other networked machines.  Subdirectories on
     other file systems will be ignored.

     The host name specifies which host to run ‘tar’ on, and should
     normally be the host that actually contains the file system.
     However, the host machine must have GNU ‘tar’ installed, and must
     be able to access the directory containing the backup scripts and
     their support files using the same file name that is used on the
     machine where the scripts are run (i.e., what ‘pwd’ will print when
     in that directory on that machine).  If the host that contains the
     file system does not have this capability, you can specify another
     host as long as it can access the file system through NFS.

     If the list of file systems is very long you may wish to put it in
     a separate file.  This file is usually named ‘/etc/backup/dirs’,
     but this name may be overridden in ‘backup-specs’ using ‘DIRLIST’
     variable.

 -- Backup variable: DIRLIST

     The name of the file that contains a list of file systems to backup
     or restore.  By default it is ‘/etc/backup/dirs’.

 -- Backup variable: BACKUP_FILES

     A list of individual files to be dumped (for ‘backup’), or restored
     (for ‘restore’).  These should be accessible from the machine on
     which the backup script is run.

     If the list of individual files is very long you may wish to store
     it in a separate file.  This file is usually named
     ‘/etc/backup/files’, but this name may be overridden in
     ‘backup-specs’ using ‘FILELIST’ variable.

 -- Backup variable: FILELIST

     The name of the file that contains a list of individual files to
     backup or restore.  By default it is ‘/etc/backup/files’.

 -- Backup variable: MT

     Full file name of ‘mt’ binary.

 -- Backup variable: RSH
     Full file name of ‘rsh’ binary or its equivalent.  You may wish to
     set it to ‘ssh’, to improve security.  In this case you will have
     to use public key authentication.

 -- Backup variable: RSH_COMMAND

     Full file name of ‘rsh’ binary on remote machines.  This will be
     passed via ‘--rsh-command’ option to the remote invocation of GNU
     ‘tar’.

 -- Backup variable: VOLNO_FILE

     Name of temporary file to hold volume numbers.  This needs to be
     accessible by all the machines which have file systems to be
     dumped.

 -- Backup variable: XLIST

     Name of “exclude file list”.  An “exclude file list” is a file
     located on the remote machine and containing the list of files to
     be excluded from the backup.  Exclude file lists are searched in
     /etc/tar-backup directory.  A common use for exclude file lists is
     to exclude files containing security-sensitive information (e.g.,
     ‘/etc/shadow’ from backups).

     This variable affects only ‘backup’.

 -- Backup variable: SLEEP_TIME

     Time to sleep between dumps of any two successive file systems

     This variable affects only ‘backup’.

 -- Backup variable: DUMP_REMIND_SCRIPT

     Script to be run when it’s time to insert a new tape in for the
     next volume.  Administrators may want to tailor this script for
     their site.  If this variable isn’t set, GNU ‘tar’ will display its
     built-in prompt, and will expect confirmation from the console.
     For the description of the default prompt, see *note change volume
     prompt::.

 -- Backup variable: SLEEP_MESSAGE

     Message to display on the terminal while waiting for dump time.
     Usually this will just be some literal text.

 -- Backup variable: TAR

     Full file name of the GNU ‘tar’ executable.  If this is not set,
     backup scripts will search ‘tar’ in the current shell path.


File: tar.info,  Node: Magnetic Tape Control,  Next: User Hooks,  Prev: General-Purpose Variables,  Up: Backup Parameters

5.4.2 Magnetic Tape Control
---------------------------

Backup scripts access tape device using special “hook functions”.  These
functions take a single argument — the name of the tape device.  Their
names are kept in the following variables:

 -- Backup variable: MT_BEGIN
     The name of “begin” function.  This function is called before
     accessing the drive.  By default it retensions the tape:

          MT_BEGIN=mt_begin

          mt_begin() {
              mt -f "$1" retension
          }

 -- Backup variable: MT_REWIND
     The name of “rewind” function.  The default definition is as
     follows:

          MT_REWIND=mt_rewind

          mt_rewind() {
              mt -f "$1" rewind
          }

 -- Backup variable: MT_OFFLINE
     The name of the function switching the tape off line.  By default
     it is defined as follows:

          MT_OFFLINE=mt_offline

          mt_offline() {
              mt -f "$1" offl
          }

 -- Backup variable: MT_STATUS
     The name of the function used to obtain the status of the archive
     device, including error count.  Default definition:

          MT_STATUS=mt_status

          mt_status() {
              mt -f "$1" status
          }


File: tar.info,  Node: User Hooks,  Next: backup-specs example,  Prev: Magnetic Tape Control,  Up: Backup Parameters

5.4.3 User Hooks
----------------

“User hooks” are shell functions executed before and after each ‘tar’
invocation.  Thus, there are “backup hooks”, which are executed before
and after dumping each file system, and “restore hooks”, executed before
and after restoring a file system.  Each user hook is a shell function
taking four arguments:

 -- User Hook Function: hook LEVEL HOST FS FSNAME
     Its arguments are:

     LEVEL
          Current backup or restore level.

     HOST
          Name or IP address of the host machine being dumped or
          restored.

     FS
          Full file name of the file system being dumped or restored.

     FSNAME
          File system name with directory separators replaced with
          colons.  This is useful, e.g., for creating unique files.

   Following variables keep the names of user hook functions:

 -- Backup variable: DUMP_BEGIN
     Dump begin function.  It is executed before dumping the file
     system.

 -- Backup variable: DUMP_END
     Executed after dumping the file system.

 -- Backup variable: RESTORE_BEGIN
     Executed before restoring the file system.

 -- Backup variable: RESTORE_END
     Executed after restoring the file system.


File: tar.info,  Node: backup-specs example,  Prev: User Hooks,  Up: Backup Parameters

5.4.4 An Example Text of ‘Backup-specs’
---------------------------------------

The following is an example of ‘backup-specs’:

     # site-specific parameters for file system backup.

     ADMINISTRATOR=friedman
     BACKUP_HOUR=1
     TAPE_FILE=/dev/nrsmt0

     # Use ssh instead of the less secure rsh
     RSH=/usr/bin/ssh
     RSH_COMMAND=/usr/bin/ssh

     # Override MT_STATUS function:
     my_status() {
           mts -t $TAPE_FILE
     }
     MT_STATUS=my_status

     # Disable MT_OFFLINE function
     MT_OFFLINE=:

     BLOCKING=124
     BACKUP_DIRS="
             albert:/fs/fsf
             apple-gunkies:/gd
             albert:/fs/gd2
             albert:/fs/gp
             geech:/usr/jla
             churchy:/usr/roland
             albert:/
             albert:/usr
             apple-gunkies:/
             apple-gunkies:/usr
             gnu:/hack
             gnu:/u
             apple-gunkies:/com/mailer/gnu
             apple-gunkies:/com/archive/gnu"

     BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"



File: tar.info,  Node: Scripted Backups,  Next: Scripted Restoration,  Prev: Backup Parameters,  Up: Backups

5.5 Using the Backup Scripts
============================

The syntax for running a backup script is:

     backup --level=LEVEL --time=TIME

   The ‘--level’ option requests the dump level.  Thus, to produce a
full dump, specify ‘--level=0’ (this is the default, so ‘--level’ may be
omitted if its value is ‘0’)(1).

   The ‘--time’ option determines when should the backup be run.  TIME
may take three forms:

HH:MM

     The dump must be run at HH hours MM minutes.

HH

     The dump must be run at HH hours.

now

     The dump must be run immediately.

   You should start a script with a tape or disk mounted.  Once you
start a script, it prompts you for new tapes or disks as it needs them.
Media volumes don’t have to correspond to archive files — a multi-volume
archive can be started in the middle of a tape that already contains the
end of another multi-volume archive.  The ‘restore’ script prompts for
media by its archive volume, so to avoid an error message you should
keep track of which tape (or disk) contains which volume of the archive
(*note Scripted Restoration::).

   The backup scripts write two files on the file system.  The first is
a record file in ‘/etc/tar-backup/’, which is used by the scripts to
store and retrieve information about which files were dumped.  This file
is not meant to be read by humans, and should not be deleted by them.
*Note Snapshot Files::, for a more detailed explanation of this file.

   The second file is a log file containing the names of the file
systems and files dumped, what time the backup was made, and any error
messages that were generated, as well as how much space was left in the
media volume after the last volume of the archive was written.  You
should check this log file after every backup.  The file name is
‘log-MM-DD-YYYY-level-N’, where MM-DD-YYYY represents current date, and
N represents current dump level number.

   The script also prints the name of each system being dumped to the
standard output.

   Following is the full list of options accepted by ‘backup’ script:

‘-l LEVEL’
‘--level=LEVEL’
     Do backup level LEVEL (default 0).

‘-f’
‘--force’
     Force backup even if today’s log file already exists.

‘-v[LEVEL]’
‘--verbose[=LEVEL]’
     Set verbosity level.  The higher the level is, the more debugging
     information will be output during execution.  Default LEVEL is 100,
     which means the highest debugging level.

‘-t START-TIME’
‘--time=START-TIME’
     Wait till TIME, then do backup.

‘-h’
‘--help’
     Display short help message and exit.

‘-V’
‘--version’
     Display information about the program’s name, version, origin and
     legal status, all on standard output, and then exit successfully.

   ---------- Footnotes ----------

   (1) For backward compatibility, the ‘backup’ will also try to deduce
the requested dump level from the name of the script itself.  If the
name consists of a string ‘level-’ followed by a single decimal digit,
that digit is taken as the dump level number.  Thus, you may create a
link from ‘backup’ to ‘level-1’ and then run ‘level-1’ whenever you need
to create a level one dump.


File: tar.info,  Node: Scripted Restoration,  Prev: Scripted Backups,  Up: Backups

5.6 Using the Restore Script
============================

To restore files that were archived using a scripted backup, use the
‘restore’ script.  Its usage is quite straightforward.  In the simplest
form, invoke ‘restore --all’, it will then restore all the file systems
and files specified in ‘backup-specs’ (*note BACKUP_DIRS:
General-Purpose Variables.).

   You may select the file systems (and/or files) to restore by giving
‘restore’ a list of “patterns” in its command line.  For example,
running

     restore 'albert:*'

will restore all file systems on the machine ‘albert’.  A more
complicated example:

     restore 'albert:*' '*:/var'

This command will restore all file systems on the machine ‘albert’ as
well as ‘/var’ file system on all machines.

   By default ‘restore’ will start restoring files from the lowest
available dump level (usually zero) and will continue through all
available dump levels.  There may be situations where such a thorough
restore is not necessary.  For example, you may wish to restore only
files from the recent level one backup.  To do so, use ‘--level’ option,
as shown in the example below:

     restore --level=1

   The full list of options accepted by ‘restore’ follows:

‘-a’
‘--all’
     Restore all file systems and files specified in ‘backup-specs’.

‘-l LEVEL’
‘--level=LEVEL’
     Start restoring from the given backup level, instead of the default
     0.

‘-v[LEVEL]’
‘--verbose[=LEVEL]’
     Set verbosity level.  The higher the level is, the more debugging
     information will be output during execution.  Default LEVEL is 100,
     which means the highest debugging level.

‘-h’
‘--help’
     Display short help message and exit.

‘-V’
‘--version’
     Display information about the program’s name, version, origin and
     legal status, all on standard output, and then exit successfully.

   You should start the restore script with the media containing the
first volume of the archive mounted.  The script will prompt for other
volumes as they are needed.  If the archive is on tape, you don’t need
to rewind the tape to to its beginning—if the tape head is positioned
past the beginning of the archive, the script will rewind the tape as
needed.  *Note Tape Positioning::, for a discussion of tape positioning.

     *Warning:* The script will delete files from the active file system
     if they were not in the file system when the archive was made.

   *Note Incremental Dumps::, for an explanation of how the script makes
that determination.


File: tar.info,  Node: Choosing,  Next: Date input formats,  Prev: Backups,  Up: Top

6 Choosing Files and Names for ‘tar’
************************************

Certain options to ‘tar’ enable you to specify a name for your archive.
Other options let you decide which files to include or exclude from the
archive, based on when or whether files were modified, whether the file
names do or don’t match specified patterns, or whether files are in
specified directories.

   This chapter discusses these options in detail.

* Menu:

* file::                        Choosing the Archive’s Name
* Selecting Archive Members::
* files::                       Reading Names from a File
* exclude::                     Excluding Some Files
* wildcards::                   Wildcards Patterns and Matching
* quoting styles::              Ways of Quoting Special Characters in Names
* transform::                   Modifying File and Member Names
* after::                       Operating Only on New Files
* recurse::                     Descending into Directories
* one::                         Crossing File System Boundaries


File: tar.info,  Node: file,  Next: Selecting Archive Members,  Up: Choosing

6.1 Choosing and Naming Archive Files
=====================================

By default, ‘tar’ uses an archive file name that was compiled when it
was built on the system; usually this name refers to some physical tape
drive on the machine.  However, the person who installed ‘tar’ on the
system may not have set the default to a meaningful value as far as most
users are concerned.  As a result, you will usually want to tell ‘tar’
where to find (or create) the archive.  The ‘--file=ARCHIVE-NAME’ (‘-f
ARCHIVE-NAME’) option allows you to either specify or name a file to use
as the archive instead of the default archive file location.

‘--file=ARCHIVE-NAME’
‘-f ARCHIVE-NAME’
     Name the archive to create or operate on.  Use in conjunction with
     any operation.

   For example, in this ‘tar’ command,

     $ tar -cvf collection.tar blues folk jazz

‘collection.tar’ is the name of the archive.  It must directly follow
the ‘-f’ option, since whatever directly follows ‘-f’ _will_ end up
naming the archive.  If you neglect to specify an archive name, you may
end up overwriting a file in the working directory with the archive you
create since ‘tar’ will use this file’s name for the archive name.

   An archive can be saved as a file in the file system, sent through a
pipe or over a network, or written to an I/O device such as a tape,
floppy disk, or CD write drive.

   If you do not name the archive, ‘tar’ uses the value of the
environment variable ‘TAPE’ as the file name for the archive.  If that
is not available, ‘tar’ uses a default, compiled-in archive name,
usually that for tape unit zero (i.e., ‘/dev/tu00’).

   If you use ‘-’ as an ARCHIVE-NAME, ‘tar’ reads the archive from
standard input (when listing or extracting files), or writes it to
standard output (when creating an archive).  If you use ‘-’ as an
ARCHIVE-NAME when modifying an archive, ‘tar’ reads the original archive
from its standard input and writes the entire new archive to its
standard output.

   The following example is a convenient way of copying directory
hierarchy from ‘sourcedir’ to ‘targetdir’.

     $ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)

   The ‘-C’ option allows to avoid using subshells:

     $ tar -C sourcedir -cf - . | tar -C targetdir -xpf -

   In both examples above, the leftmost ‘tar’ invocation archives the
contents of ‘sourcedir’ to the standard output, while the rightmost one
reads this archive from its standard input and extracts it.  The ‘-p’
option tells it to restore permissions of the extracted files.

   To specify an archive file on a device attached to a remote machine,
use the following:

     --file=HOSTNAME:/DEV/FILE-NAME

‘tar’ will set up the remote connection, if possible, and prompt you for
a username and password.  If you use ‘--file=@HOSTNAME:/DEV/FILE-NAME’,
‘tar’ will attempt to set up the remote connection using your username
as the username on the remote machine.

   If the archive file name includes a colon (‘:’), then it is assumed
to be a file on another machine.  If the archive file is
‘USER@HOST:FILE’, then FILE is used on the host HOST.  The remote host
is accessed using the ‘rsh’ program, with a username of USER.  If the
username is omitted (along with the ‘@’ sign), then your user name will
be used.  (This is the normal ‘rsh’ behavior.)  It is necessary for the
remote machine, in addition to permitting your ‘rsh’ access, to have the
‘rmt’ program installed (this command is included in the GNU ‘tar’
distribution and by default is installed under ‘PREFIX/libexec/rmt’,
where PREFIX means your installation prefix).  If you need to use a file
whose name includes a colon, then the remote tape drive behavior can be
inhibited by using the ‘--force-local’ option.

   When the archive is being created to ‘/dev/null’, GNU ‘tar’ tries to
minimize input and output operations.  The Amanda backup system, when
used with GNU ‘tar’, has an initial sizing pass which uses this feature.


File: tar.info,  Node: Selecting Archive Members,  Next: files,  Prev: file,  Up: Choosing

6.2 Selecting Archive Members
=============================

“File Name arguments” specify which files in the file system ‘tar’
operates on, when creating or adding to an archive, or which archive
members ‘tar’ operates on, when reading or deleting from an archive.
*Note Operations::.

   To specify file names, you can include them as the last arguments on
the command line, as follows:
     tar OPERATION [OPTION1 OPTION2 ...] [FILE NAME-1 FILE NAME-2 ...]

   If a file name begins with dash (‘-’), precede it with ‘--add-file’
option to prevent it from being treated as an option.

   By default GNU ‘tar’ attempts to “unquote” each file or member name,
replacing “escape sequences” according to the following table:

Escape         Replaced with
-----------------------------------------------------------
\a             Audible bell (ASCII 7)
\b             Backspace (ASCII 8)
\f             Form feed (ASCII 12)
\n             New line (ASCII 10)
\r             Carriage return (ASCII 13)
\t             Horizontal tabulation (ASCII 9)
\v             Vertical tabulation (ASCII 11)
\?             ASCII 127
\N             ASCII N (N should be an octal number of
               up to 3 digits)

   A backslash followed by any other symbol is retained.

   This default behavior is controlled by the following command line
option:

‘--unquote’
     Enable unquoting input file or member names (default).

‘--no-unquote’
     Disable unquoting input file or member names.

   If you specify a directory name as a file name argument, all the
files in that directory are operated on by ‘tar’.

   If you do not specify files, ‘tar’ behavior differs depending on the
operation mode as described below:

   When ‘tar’ is invoked with ‘--create’ (‘-c’), ‘tar’ will stop
immediately, reporting the following:

     $ tar cf a.tar
     tar: Cowardly refusing to create an empty archive
     Try 'tar --help' or 'tar --usage' for more information.

   If you specify either ‘--list’ (‘-t’) or ‘--extract’ (‘--get’, ‘-x’),
‘tar’ operates on all the archive members in the archive.

   If run with ‘--diff’ option, tar will compare the archive with the
contents of the current working directory.

   If you specify any other operation, ‘tar’ does nothing.

   By default, ‘tar’ takes file names from the command line.  However,
there are other ways to specify file or member names, or to modify the
manner in which ‘tar’ selects the files or members upon which to
operate.  In general, these methods work both for specifying the names
of files and archive members.


File: tar.info,  Node: files,  Next: exclude,  Prev: Selecting Archive Members,  Up: Choosing

6.3 Reading Names from a File
=============================

Instead of giving the names of files or archive members on the command
line, you can put the names into a file, and then use the
‘--files-from=FILE-OF-NAMES’ (‘-T FILE-OF-NAMES’) option to ‘tar’.  Give
the name of the file which contains the list of files to include as the
argument to ‘--files-from’.  In the list, the file names should be
separated by newlines.  You will frequently use this option when you
have generated the list of files to archive with the ‘find’ utility.

‘--files-from=FILE-NAME’
‘-T FILE-NAME’
     Get names to extract or create from file FILE-NAME.

   If you give a single dash as a file name for ‘--files-from’, (i.e.,
you specify either ‘--files-from=-’ or ‘-T -’), then the file names are
read from standard input.

   Unless you are running ‘tar’ with ‘--create’, you cannot use both
‘--files-from=-’ and ‘--file=-’ (‘-f -’) in the same command.

   Any number of ‘-T’ options can be given in the command line.

   The following example shows how to use ‘find’ to generate a list of
files smaller than 400 blocks in length(1) and put that list into a file
called ‘small-files’.  You can then use the ‘-T’ option to ‘tar’ to
specify the files from that file, ‘small-files’, to create the archive
‘little.tgz’.  (The ‘-z’ option to ‘tar’ compresses the archive with
‘gzip’; *note gzip:: for more information.)

     $ find . -size -400 -print > small-files
     $ tar -c -v -z -T small-files -f little.tgz

By default, each line read from the file list is first stripped off any
leading and trailing whitespace.  If the resulting string begins with
‘-’ character, it is considered a ‘tar’ option and is processed
accordingly(2).  Only a subset of GNU ‘tar’ options is allowed for use
in file lists.  For a list of such options, *note Position-Sensitive
Options::.

   For example, the common use of this feature is to change to another
directory by specifying ‘-C’ option:

     $ cat list
     -C/etc
     passwd
     hosts
     -C/lib
     libc.a
     $ tar -c -f foo.tar --files-from list

In this example, ‘tar’ will first switch to ‘/etc’ directory and add
files ‘passwd’ and ‘hosts’ to the archive.  Then it will change to
‘/lib’ directory and will archive the file ‘libc.a’.  Thus, the
resulting archive ‘foo.tar’ will contain:

     $ tar tf foo.tar
     passwd
     hosts
     libc.a

   Note, that any options used in the file list remain in effect for the
rest of the command line.  For example, using the same ‘list’ file as
above, the following command

     $ tar -c -f foo.tar --files-from list libcurses.a

will look for file ‘libcurses.a’ in the directory ‘/lib’, because it was
used with the last ‘-C’ option (*note Position-Sensitive Options::).

   If such option handling is undesirable, use the
‘--verbatim-files-from’ option.  When this option is in effect, each
line read from the file list is treated as a file name.  Notice, that
this means, in particular, that no whitespace trimming is performed.

   The ‘--verbatim-files-from’ affects all ‘-T’ options that follow it
in the command line.  The default behavior can be restored using
‘--no-verbatim-files-from’ option.

   To disable option handling for a single file name, use the
‘--add-file’ option, e.g.: ‘--add-file=--my-file’.

   You can use any GNU ‘tar’ command line options in the file list file,
including ‘--files-from’ option itself.  This allows for including
contents of a file list into another file list file.  Note however, that
options that control file list processing, such as
‘--verbatim-files-from’ or ‘--null’ won’t affect the file they appear
in.  They will affect next ‘--files-from’ option, if there is any.

* Menu:

* nul::

   ---------- Footnotes ----------

   (1) A file system block is usually 512 bytes, so this amounts to
200K. Use the ‘c’ suffix to specify size in _bytes_.  Also, when using
GNU find, you can specify other size units, such as ‘k’, ‘m’, etc.
*Note (find.info)Size::, for details.

   (2) Versions of GNU ‘tar’ up to 1.15.1 recognized only ‘-C’ option in
file lists, and only if the option and its argument occupied two
consecutive lines.


File: tar.info,  Node: nul,  Up: files

6.3.1 ‘NUL’-Terminated File Names
---------------------------------

The ‘--null’ option causes ‘--files-from=FILE-OF-NAMES’ (‘-T
FILE-OF-NAMES’) to read file names terminated by a ‘NUL’ instead of a
newline, so files whose names contain newlines can be archived using
‘--files-from’.

‘--null’
     Only consider ‘NUL’-terminated file names, instead of files that
     terminate in a newline.

‘--no-null’
     Undo the effect of any previous ‘--null’ option.

   The ‘--null’ option is just like the one in GNU ‘xargs’ and ‘cpio’,
and is useful with the ‘-print0’ predicate of GNU ‘find’.  In ‘tar’,
‘--null’ also disables special handling for file names that begin with
dash (similar to ‘--verbatim-files-from’ option).

   This example shows how to use ‘find’ to generate a list of files
larger than 800 blocks in length and put that list into a file called
‘long-files’.  The ‘-print0’ option to ‘find’ is just like ‘-print’,
except that it separates files with a ‘NUL’ rather than with a newline.
You can then run ‘tar’ with both the ‘--null’ and ‘-T’ options to
specify that ‘tar’ gets the files from that file, ‘long-files’, to
create the archive ‘big.tgz’.  The ‘--null’ option to ‘tar’ will cause
‘tar’ to recognize the ‘NUL’ separator between files.

     $ find . -size +800 -print0 > long-files
     $ tar -c -v --null --files-from=long-files --file=big.tar

   The ‘--no-null’ option can be used if you need to read both
‘NUL’-terminated and newline-terminated files on the same command line.
For example, if ‘flist’ is a newline-terminated file, then the following
command can be used to combine it with the above command:

     $ find . -size +800 -print0 |
       tar -c -f big.tar --null -T - --no-null -T flist

   This example uses short options for typographic reasons, to avoid
very long lines.

   GNU ‘tar’ is tries to automatically detect ‘NUL’-terminated file
lists, so in many cases it is safe to use them even without the ‘--null’
option.  In this case ‘tar’ will print a warning and continue reading
such a file as if ‘--null’ were actually given:

     $ find . -size +800 -print0 | tar -c -f big.tar -T -
     tar: -: file name read contains nul character

   The null terminator, however, remains in effect only for this
particular file, any following ‘-T’ options will assume newline
termination.  Of course, the null autodetection applies to these
eventual surplus ‘-T’ options as well.


File: tar.info,  Node: exclude,  Next: wildcards,  Prev: files,  Up: Choosing

6.4 Excluding Some Files
========================

To avoid operating on files whose names match a particular pattern, use
the ‘--exclude’ or ‘--exclude-from’ options.

‘--exclude=PATTERN’
     Causes ‘tar’ to ignore files that match the PATTERN.

   The ‘--exclude=PATTERN’ option prevents any file or member whose name
matches the shell wildcard (PATTERN) from being operated on.  For
example, to create an archive with all the contents of the directory
‘src’ except for files whose names end in ‘.o’, use the command ‘tar -cf
src.tar --exclude='*.o' src’.

   You may give multiple ‘--exclude’ options.

‘--exclude-from=FILE’
‘-X FILE’
     Causes ‘tar’ to ignore files that match the patterns listed in
     FILE.

   Use the ‘--exclude-from’ option to read a list of patterns, one per
line, from FILE; ‘tar’ will ignore files matching those patterns.  Thus
if ‘tar’ is called as ‘tar -c -X foo .’ and the file ‘foo’ contains a
single line ‘*.o’, no files whose names end in ‘.o’ will be added to the
archive.

   Notice, that lines from FILE are read verbatim.  One of the frequent
errors is leaving some extra whitespace after a file name, which is
difficult to catch using text editors.

   However, empty lines are OK.

   When archiving directories that are under some version control system
(VCS), it is often convenient to read exclusion patterns from this VCS’
ignore files (e.g.  ‘.cvsignore’, ‘.gitignore’, etc.)  The following
options provide such possibility:

‘--exclude-vcs-ignores’
     Before archiving a directory, see if it contains any of the
     following files: ‘cvsignore’, ‘.gitignore’, ‘.bzrignore’, or
     ‘.hgignore’.  If so, read ignore patterns from these files.

     The patterns are treated much as the corresponding VCS would treat
     them, i.e.:

     ‘.cvsignore’
          Contains shell-style globbing patterns that apply only to the
          directory where this file resides.  No comments are allowed in
          the file.  Empty lines are ignored.

     ‘.gitignore’
          Contains shell-style globbing patterns.  Applies to the
          directory where ‘.gitfile’ is located and all its
          subdirectories.

          Any line beginning with a ‘#’ is a comment.  Backslash escapes
          the comment character.

     ‘.bzrignore’
          Contains shell globbing-patterns and regular expressions (if
          prefixed with ‘RE:’(1).  Patterns affect the directory and all
          its subdirectories.

          Any line beginning with a ‘#’ is a comment.

     ‘.hgignore’
          Contains posix regular expressions(2).  The line ‘syntax:
          glob’ switches to shell globbing patterns.  The line ‘syntax:
          regexp’ switches back.  Comments begin with a ‘#’.  Patterns
          affect the directory and all its subdirectories.

‘--exclude-ignore=FILE’
     Before dumping a directory, ‘tar’ checks if it contains FILE.  If
     so, exclusion patterns are read from this file.  The patterns
     affect only the directory itself.

‘--exclude-ignore-recursive=FILE’
     Same as ‘--exclude-ignore’, except that the patterns read affect
     both the directory where FILE resides and all its subdirectories.

‘--exclude-vcs’
     Exclude files and directories used by following version control
     systems: ‘CVS’, ‘RCS’, ‘SCCS’, ‘SVN’, ‘Arch’, ‘Bazaar’,
     ‘Mercurial’, and ‘Darcs’.

     As of version 1.35, the following files are excluded:

        • ‘CVS/’, and everything under it
        • ‘RCS/’, and everything under it
        • ‘SCCS/’, and everything under it
        • ‘.git/’, and everything under it
        • ‘.gitignore’
        • ‘.gitmodules’
        • ‘.gitattributes’
        • ‘.cvsignore’
        • ‘.svn/’, and everything under it
        • ‘.arch-ids/’, and everything under it
        • ‘{arch}/’, and everything under it
        • ‘=RELEASE-ID’
        • ‘=meta-update’
        • ‘=update’
        • ‘.bzr’
        • ‘.bzrignore’
        • ‘.bzrtags’
        • ‘.hg’
        • ‘.hgignore’
        • ‘.hgrags’
        • ‘_darcs’

‘--exclude-backups’
     Exclude backup and lock files.  This option causes exclusion of
     files that match the following shell globbing patterns:

     .#*
     *~
     #*#

   When creating an archive, the ‘--exclude-caches’ option family causes
‘tar’ to exclude all directories that contain a “cache directory tag”.
A cache directory tag is a short file with the well-known name
‘CACHEDIR.TAG’ and having a standard header specified in
<http://www.brynosaurus.com/cachedir/spec.html>.  Various applications
write cache directory tags into directories they use to hold
regenerable, non-precious data, so that such data can be more easily
excluded from backups.

   There are three ‘exclude-caches’ options, each providing a different
exclusion semantics:

‘--exclude-caches’
     Do not archive the contents of the directory, but archive the
     directory itself and the ‘CACHEDIR.TAG’ file.

‘--exclude-caches-under’
     Do not archive the contents of the directory, nor the
     ‘CACHEDIR.TAG’ file, archive only the directory itself.

‘--exclude-caches-all’
     Omit directories containing ‘CACHEDIR.TAG’ file entirely.

   Another option family, ‘--exclude-tag’, provides a generalization of
this concept.  It takes a single argument, a file name to look for.  Any
directory that contains this file will be excluded from the dump.
Similarly to ‘exclude-caches’, there are three options in this option
family:

‘--exclude-tag=FILE’
     Do not dump the contents of the directory, but dump the directory
     itself and the FILE.

‘--exclude-tag-under=FILE’
     Do not dump the contents of the directory, nor the FILE, archive
     only the directory itself.

‘--exclude-tag-all=FILE’
     Omit directories containing FILE file entirely.

   Multiple ‘--exclude-tag*’ options can be given.

   For example, given this directory:

     $ find dir
     dir
     dir/blues
     dir/jazz
     dir/folk
     dir/folk/tagfile
     dir/folk/sanjuan
     dir/folk/trote

   The ‘--exclude-tag’ will produce the following:

     $ tar -cf archive.tar --exclude-tag=tagfile -v dir
     dir/
     dir/blues
     dir/jazz
     dir/folk/
     tar: dir/folk/: contains a cache directory tag tagfile;
       contents not dumped
     dir/folk/tagfile

   Both the ‘dir/folk’ directory and its tagfile are preserved in the
archive, however the rest of files in this directory are not.

   Now, using the ‘--exclude-tag-under’ option will exclude ‘tagfile’
from the dump, while still preserving the directory itself, as shown in
this example:

     $ tar -cf archive.tar --exclude-tag-under=tagfile -v dir
     dir/
     dir/blues
     dir/jazz
     dir/folk/
     ./tar: dir/folk/: contains a cache directory tag tagfile;
       contents not dumped

   Finally, using ‘--exclude-tag-all’ omits the ‘dir/folk’ directory
entirely:

     $ tar -cf archive.tar --exclude-tag-all=tagfile -v dir
     dir/
     dir/blues
     dir/jazz
     ./tar: dir/folk/: contains a cache directory tag tagfile;
       directory not dumped

* Menu:

* problems with exclude::

   ---------- Footnotes ----------

   (1) According to the Bazaar docs, globbing-patterns are Korn-shell
style and regular expressions are perl-style.  As of GNU ‘tar’ version
1.35, these are treated as shell-style globs and posix extended regexps.
This will be fixed in future releases.

   (2) Support for perl-style regexps will appear in future releases.


File: tar.info,  Node: problems with exclude,  Up: exclude

Problems with Using the ‘exclude’ Options
-----------------------------------------

Some users find ‘exclude’ options confusing.  Here are some common
pitfalls:

   • The main operating mode of ‘tar’ does not act on a file name
     explicitly listed on the command line, if one of its file name
     components is excluded.  In the example above, if you create an
     archive and exclude files that end with ‘*.o’, but explicitly name
     the file ‘dir.o/foo’ after all the options have been listed,
     ‘dir.o/foo’ will be excluded from the archive.

   • You can sometimes confuse the meanings of ‘--exclude’ and
     ‘--exclude-from’.  Be careful: use ‘--exclude’ when files to be
     excluded are given as a pattern on the command line.  Use
     ‘--exclude-from’ to introduce the name of a file which contains a
     list of patterns, one per line; each of these patterns can exclude
     zero, one, or many files.

   • When you use ‘--exclude=PATTERN’, be sure to quote the PATTERN
     parameter, so GNU ‘tar’ sees wildcard characters like ‘*’.  If you
     do not do this, the shell might expand the ‘*’ itself using files
     at hand, so ‘tar’ might receive a list of files instead of one
     pattern, or none at all, making the command somewhat illegal.  This
     might not correspond to what you want.

     For example, write:

          $ tar -c -f ARCHIVE.TAR --exclude '*.o' DIRECTORY

     rather than:

          # _Wrong!_
          $ tar -c -f ARCHIVE.TAR --exclude *.o DIRECTORY

   • You must use use shell syntax, or globbing, rather than ‘regexp’
     syntax, when using exclude options in ‘tar’.  If you try to use
     ‘regexp’ syntax to describe files to be excluded, your command
     might fail.

   • 
     In earlier versions of ‘tar’, what is now the ‘--exclude-from’
     option was called ‘--exclude’ instead.  Now, ‘--exclude’ applies to
     patterns listed on the command line and ‘--exclude-from’ applies to
     patterns listed in a file.


File: tar.info,  Node: wildcards,  Next: quoting styles,  Prev: exclude,  Up: Choosing

6.5 Wildcards Patterns and Matching
===================================

“Globbing” is the operation by which “wildcard” characters, ‘*’ or ‘?’
for example, are replaced and expanded into all existing files matching
the given pattern.  GNU ‘tar’ can use wildcard patterns for matching (or
globbing) archive members when extracting from or listing an archive.
Wildcard patterns are also used for verifying volume labels of ‘tar’
archives.  This section has the purpose of explaining wildcard syntax
for ‘tar’.

   A PATTERN should be written according to shell syntax, using wildcard
characters to effect globbing.  Most characters in the pattern stand for
themselves in the matched string, and case is significant: ‘a’ will
match only ‘a’, and not ‘A’.  The character ‘?’ in the pattern matches
any single character in the matched string.  The character ‘*’ in the
pattern matches zero, one, or more single characters in the matched
string.  The character ‘\’ says to take the following character of the
pattern _literally_; it is useful when one needs to match the ‘?’, ‘*’,
‘[’ or ‘\’ characters, themselves.

   The character ‘[’, up to the matching ‘]’, introduces a character
class.  A “character class” is a list of acceptable characters for the
next single character of the matched string.  For example, ‘[abcde]’
would match any of the first five letters of the alphabet.  Note that
within a character class, all of the “special characters” listed above
other than ‘\’ lose their special meaning; for example, ‘[-\\[*?]]’
would match any of the characters, ‘-’, ‘\’, ‘[’, ‘*’, ‘?’, or ‘]’.
(Due to parsing constraints, the characters ‘-’ and ‘]’ must either come
_first_ or _last_ in a character class.)

   If the first character of the class after the opening ‘[’ is ‘!’ or
‘^’, then the meaning of the class is reversed.  Rather than listing
character to match, it lists those characters which are _forbidden_ as
the next single character of the matched string.

   Other characters of the class stand for themselves.  The special
construction ‘[A-E]’, using an hyphen between two letters, is meant to
represent all characters between A and E, inclusive.

   Periods (‘.’) or forward slashes (‘/’) are not considered special for
wildcard matches.  However, if a pattern completely matches a directory
prefix of a matched string, then it matches the full matched string:
thus, excluding a directory also excludes all the files beneath it.

* Menu:

* controlling pattern-matching::


File: tar.info,  Node: controlling pattern-matching,  Up: wildcards

Controlling Pattern-Matching
----------------------------

For the purposes of this section, we call “exclusion members” all member
names obtained while processing ‘--exclude’ and ‘--exclude-from’
options, and “inclusion members” those member names that were given in
the command line or read from the file specified with ‘--files-from’
option.

   These two pairs of member lists are used in the following operations:
‘--diff’, ‘--extract’, ‘--list’, ‘--update’.

   There are no inclusion members in create mode (‘--create’ and
‘--append’), since in this mode the names obtained from the command line
refer to _files_, not archive members.

   By default, inclusion members are compared with archive members
literally (1) and exclusion members are treated as globbing patterns.
For example:

     $ tar tf foo.tar
     a.c
     b.c
     a.txt
     [remarks]
     # Member names are used verbatim:
     $ tar -xf foo.tar -v '[remarks]'
     [remarks]
     # Exclude member names are globbed:
     $ tar -xf foo.tar -v --exclude '*.c'
     a.txt
     [remarks]

   This behavior can be altered by using the following options:

‘--wildcards’
     Treat all member names as wildcards.

‘--no-wildcards’
     Treat all member names as literal strings.

   Thus, to extract files whose names end in ‘.c’, you can use:

     $ tar -xf foo.tar -v --wildcards '*.c'
     a.c
     b.c

Notice quoting of the pattern to prevent the shell from interpreting it.

   The effect of ‘--wildcards’ option is canceled by ‘--no-wildcards’.
This can be used to pass part of the command line arguments verbatim and
other part as globbing patterns.  For example, the following invocation:

     $ tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'

instructs ‘tar’ to extract from ‘foo.tar’ all files whose names end in
‘.txt’ and the file named ‘[remarks]’.

   Normally, a pattern matches a name if an initial subsequence of the
name’s components matches the pattern, where ‘*’, ‘?’, and ‘[...]’ are
the usual shell wildcards, ‘\’ escapes wildcards, and wildcards can
match ‘/’.

   Other than optionally stripping leading ‘/’ from names (*note
absolute::), patterns and names are used as-is.  For example, trailing
‘/’ is not trimmed from a user-specified name before deciding whether to
exclude it.

   However, this matching procedure can be altered by the options listed
below.  These options accumulate.  For example:

     --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'

ignores case when excluding ‘makefile’, but not when excluding ‘readme’.

‘--anchored’
‘--no-anchored’
     If anchored, a pattern must match an initial subsequence of the
     name’s components.  Otherwise, the pattern can match any
     subsequence.  Default is ‘--no-anchored’ for exclusion members and
     ‘--anchored’ inclusion members.

‘--ignore-case’
‘--no-ignore-case’
     When ignoring case, upper-case patterns match lower-case names and
     vice versa.  When not ignoring case (the default), matching is
     case-sensitive.

‘--wildcards-match-slash’
‘--no-wildcards-match-slash’
     When wildcards match slash (the default for exclusion members), a
     wildcard like ‘*’ in the pattern can match a ‘/’ in the name.
     Otherwise, ‘/’ is matched only by ‘/’.

   The ‘--recursion’ and ‘--no-recursion’ options (*note recurse::) also
affect how member patterns are interpreted.  If recursion is in effect,
a pattern matches a name if it matches any of the name’s parent
directories.

   The following table summarizes pattern-matching default values:

Members                Default settings
--------------------------------------------------------------------------
Inclusion              ‘--no-wildcards --anchored
                       --no-wildcards-match-slash’
Exclusion              ‘--wildcards --no-anchored
                       --wildcards-match-slash’

   ---------- Footnotes ----------

   (1) Notice that earlier GNU ‘tar’ versions used globbing for
inclusion members, which contradicted to UNIX98 specification and was
not documented.  *Note Changes::, for more information on this and other
changes.


File: tar.info,  Node: quoting styles,  Next: transform,  Prev: wildcards,  Up: Choosing

6.6 Quoting Member Names
========================

When displaying member names, ‘tar’ takes care to avoid ambiguities
caused by certain characters.  This is called “name quoting”.  The
characters in question are:

   • Non-printable control characters:
     Character      ASCII   Character name
     -------------------------------------------------------------------
     \a             7       Audible bell
     \b             8       Backspace
     \f             12      Form feed
     \n             10      New line
     \r             13      Carriage return
     \t             9       Horizontal tabulation
     \v             11      Vertical tabulation

   • Space (ASCII 32)

   • Single and double quotes (‘'’ and ‘"’)

   • Backslash (‘\’)

   The exact way ‘tar’ uses to quote these characters depends on the
“quoting style”.  The default quoting style, called “escape” (see
below), uses backslash notation to represent control characters and
backslash.

   GNU ‘tar’ offers seven distinct quoting styles, which can be selected
using ‘--quoting-style’ option:

‘--quoting-style=STYLE’

     Sets quoting style.  Valid values for STYLE argument are: literal,
     shell, shell-always, c, escape, locale, clocale.

   These styles are described in detail below.  To illustrate their
effect, we will use an imaginary tar archive ‘arch.tar’ containing the
following members:

     # 1. Contains horizontal tabulation character.
     a       tab
     # 2. Contains newline character
     a
     newline
     # 3. Contains a space
     a space
     # 4. Contains double quotes
     a"double"quote
     # 5. Contains single quotes
     a'single'quote
     # 6. Contains a backslash character:
     a\backslash

   Here is how usual ‘ls’ command would have listed them, if they had
existed in the current working directory:

     $ ls
     a\ttab
     a\nnewline
     a\ space
     a"double"quote
     a'single'quote
     a\\backslash

   Quoting styles:

‘literal’
     No quoting, display each character as is:

          $ tar tf arch.tar --quoting-style=literal
          ./
          ./a space
          ./a'single'quote
          ./a"double"quote
          ./a\backslash
          ./a     tab
          ./a
          newline

‘shell’
     Display characters the same way Bourne shell does: control
     characters, except ‘\t’ and ‘\n’, are printed using backslash
     escapes, ‘\t’ and ‘\n’ are printed as is, and a single quote is
     printed as ‘\'’.  If a name contains any quoted characters, it is
     enclosed in single quotes.  In particular, if a name contains
     single quotes, it is printed as several single-quoted strings:

          $ tar tf arch.tar --quoting-style=shell
          ./
          './a space'
          './a'\''single'\''quote'
          './a"double"quote'
          './a\backslash'
          './a    tab'
          './a
          newline'

‘shell-always’
     Same as ‘shell’, but the names are always enclosed in single
     quotes:

          $ tar tf arch.tar --quoting-style=shell-always
          './'
          './a space'
          './a'\''single'\''quote'
          './a"double"quote'
          './a\backslash'
          './a    tab'
          './a
          newline'

‘c’
     Use the notation of the C programming language.  All names are
     enclosed in double quotes.  Control characters are quoted using
     backslash notations, double quotes are represented as ‘\"’,
     backslash characters are represented as ‘\\’.  Single quotes and
     spaces are not quoted:

          $ tar tf arch.tar --quoting-style=c
          "./"
          "./a space"
          "./a'single'quote"
          "./a\"double\"quote"
          "./a\\backslash"
          "./a\ttab"
          "./a\nnewline"

‘escape’
     Control characters are printed using backslash notation, and a
     backslash as ‘\\’.  This is the default quoting style, unless it
     was changed when configured the package.

          $ tar tf arch.tar --quoting-style=escape
          ./
          ./a space
          ./a'single'quote
          ./a"double"quote
          ./a\\backslash
          ./a\ttab
          ./a\nnewline

‘locale’
     Control characters, single quote and backslash are printed using
     backslash notation.  All names are quoted using left and right
     quotation marks, appropriate to the current locale.  If it does not
     define quotation marks, use ‘'’ as left and as right quotation
     marks.  Any occurrences of the right quotation mark in a name are
     escaped with ‘\’, for example:

     For example:

          $ tar tf arch.tar --quoting-style=locale
          './'
          './a space'
          './a\'single\'quote'
          './a"double"quote'
          './a\\backslash'
          './a\ttab'
          './a\nnewline'

‘clocale’
     Same as ‘locale’, but ‘"’ is used for both left and right quotation
     marks, if not provided by the currently selected locale:

          $ tar tf arch.tar --quoting-style=clocale
          "./"
          "./a space"
          "./a'single'quote"
          "./a\"double\"quote"
          "./a\\backslash"
          "./a\ttab"
          "./a\nnewline"

   You can specify which characters should be quoted in addition to
those implied by the current quoting style:

‘--quote-chars=STRING’
     Always quote characters from STRING, even if the selected quoting
     style would not quote them.

   For example, using ‘escape’ quoting (compare with the usual escape
listing above):

     $ tar tf arch.tar --quoting-style=escape --quote-chars=' "'
     ./
     ./a\ space
     ./a'single'quote
     ./a\"double\"quote
     ./a\\backslash
     ./a\ttab
     ./a\nnewline

   To disable quoting of such additional characters, use the following
option:

‘--no-quote-chars=STRING’
     Remove characters listed in STRING from the list of quoted
     characters set by the previous ‘--quote-chars’ option.

   This option is particularly useful if you have added ‘--quote-chars’
to your ‘TAR_OPTIONS’ (*note TAR_OPTIONS::) and wish to disable it for
the current invocation.

   Note, that ‘--no-quote-chars’ does _not_ disable those characters
that are quoted by default in the selected quoting style.

