GNU tar: an archiver tool ************************* This manual is for GNU `tar' (version 1.20, 14 April 2008), which creates and extracts files from archives. Copyright (C) 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001, 2003, 2004, 2005, 2006, 2007, 2008 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 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, 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. Buying copies from the FSF supports it in developing GNU and promoting software freedom." 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. 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. 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.) 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'. 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. 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. 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, Franc,ois 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'. Franc,ois 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 1.20 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 `http://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. 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. . 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. 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. 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'. 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. 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. 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.) 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 the 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::. 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 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 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. 2.6 How to Create Archives ========================== _(This message will disappear, once this node revised.)_ 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. 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. 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_. You could also say: $ tar blues --create folk --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::. 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 the remaining 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. 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 blues --create folk --file=collection.tar jazz is confusing as it is. When shown using short forms, however, it becomes much more so: $ tar blues -c folk -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. 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. 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, 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 The archive `bfiles.tar' would list as follows: ./birds baboon ./box Be sure to use a `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option just as with `--create' (`-c') to specify the name of the archive. 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: $ tar cfv archive /etc/mail tar: Removing leading `/' from member names /etc/mail/ /etc/mail/sendmail.cf /etc/mail/aliases $ tar tf archive etc/mail/ etc/mail/sendmail.cf etc/mail/aliases 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. 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=afiles.tar apple' would only print `apple'. Because `tar' preserves file names, these must be specified as they appear in the archive (i.e., relative to the directory from which the archive was created). Therefore, it is essential when specifying member names to `tar' that you give the exact member names. For example, `tar --list --file=bfiles.tar birds' would produce an error message something like `tar: birds: Not found in archive', because there is no member named `birds', only one named `./birds'. While the names `birds' and `./birds' name the same file, _member_ names by default are compared verbatim. However, `tar --list --file=bfiles.tar baboon' would respond with `baboon', because this exact member name is in the archive file `bfiles.tar'. If you are not sure of the exact file name, use "globbing patterns", for example: $ tar --list --file=bfiles.tar --wildcards '*b*' will list all members whose name contains `b'. *Note wildcards::, for a detailed discussion of globbing patterns and related `tar' command line options. 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. 2.8 How to Extract Members from an Archive ========================================== _(This message will disappear, once this node revised.)_ 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. 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-- 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 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. `tar --extract --file=bfiles.tar birds' will fail, because there is no member named `birds'. To extract the member named `./birds', you must specify `tar --extract --file=bfiles.tar ./birds'. If you don't remember the exact member names, use `--list' (`-t') option (*note list::). You can also extract those members that match a specific "globbing pattern". For example, to extract from `bfiles.tar' all files that begin with `b', no matter their directory prefix, you could type: $ tar -x -f bfiles.tar --wildcards --no-anchored 'b*' Here, `--wildcards' instructs `tar' to treat command line arguments as globbing patterns and `--no-anchored' informs it that the patterns apply to member names after any `/' delimiter. The use of globbing patterns is discussed in detail in *Note wildcards::. 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. 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. 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'). 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/folk practice/jazz practice/rock 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. 2.9 Going Further Ahead in this Manual ====================================== _(This message will disappear, once this node revised.)_ 3 Invoking GNU `tar' ******************** _(This message will disappear, once this node revised.)_ 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::). 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 is improperly written. Errors may be encountered later, while encountering an error 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 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::). 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 (two lists of four operations each 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. 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. (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.) 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. 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'. 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. 3.3.3 Old Option Style ---------------------- _(This message will disappear, once this node revised.)_ 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(1). 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'. On the other hand, this old style syntax makes 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. Old options are kept for compatibility with old versions of `tar'. 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 As far as we know, all `tar' programs, GNU and non-GNU, support old options. GNU `tar' supports them not only for historical reasons, but also because many people are used to them. For compatibility with Unix `tar', the first argument is always treated as containing command and option letters even if it doesn't start with `-'. Thus, `tar c' is equivalent to `tar -c': both of them specify the `--create' (`-c') command to create an archive. ---------- Footnotes ---------- (1) Beware that if you precede options with a dash, you are announcing the short option style instead of the old option style; short options are decoded differently. 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. 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. 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 a archive on a tape! *Note delete::. `--diff' `-d' Same `--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::. 3.4.2 `tar' Options ------------------- `--absolute-names' `-P' Normally when creating an archive, `tar' strips an initial `/' from member names. This option disables that behavior. *Note absolute::. `--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 system does not support `--atime-preserve=system', you might be able to preserve access times reliably by 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. *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 `--checklist-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'). 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::. `--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 creating a `tar' archive, `tar' will archive the file that a symbolic link points to, rather than archiving the symlink. *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-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::. `--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-tag=FILE' Exclude from dump any directory containing file named FILE, but dump the directory node and FILE itself. *Note 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::. `--exclude-tag-all=FILE' Exclude from dump any directory containing file named FILE. *Note exclude::. `--exclude-vcs' Exclude from dump directories and files, that are internal for some widely used version control systems. *Note exclude::. `--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. `--group=GROUP' Files added to the `tar' archive will have a group ID of GROUP, rather than the group from the source file. GROUP is first decoded as a group symbolic name, but if this interpretation fails, it has to be a decimal numeric group ID. *Note override::. Also see the comments for the `--owner=USER' option. `--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::. `--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 an unreadable file was encountered. *Note Reading::. `--ignore-zeros' `-i' With this option, `tar' will ignore zeroed blocks in the archive, which normally signals EOF. *Note Reading::. `--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=SCRIPT-FILE' `--new-volume-script=SCRIPT-FILE' `-F SCRIPT-FILE' When `tar' is performing multi-tape backups, SCRIPT-FILE is run at the end of each tape. If SCRIPT-FILE exits with nonzero status, `tar' fails immediately. *Note info-script::, for a detailed discussion of SCRIPT-FILE. `--interactive' `--confirmation' `-w' Specifies that `tar' should ask the user for confirmation before performing potentially destructive options, such as overwriting files. *Note interactive::. `--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. *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::. `--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::. `--lzma' This option tells `tar' to read or write archives through `lzma'. *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::. `--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-anchored' An exclude pattern can match any subsequence of the name's components. *Note controlling pattern-matching::. `--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-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-unquote' Treat all input file or member names literally, do not interpret escape sequences. *Note input name quoting::. `--no-wildcards' Do not use wildcards. *Note controlling pattern-matching::. `--no-wildcards-match-slash' Wildcards do not match `/'. *Note controlling pattern-matching::. `--null' When `tar' is using the `--files-from' option, this option instructs `tar' to expect file names terminated with NUL, so `tar' can correctly work with file names that contain newlines. *Note nul::. `--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. `--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 is first decoded as a user symbolic name, but if this interpretation fails, it has to be a decimal numeric user ID. *Note override::. This option does not affect extraction from archives. `--pax-option=KEYWORD-LIST' This option is meaningful only with POSIX.1-2001 archives (*note posix::). It 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' Synonymous with specifying both `--preserve-permissions' and `--same-order'. *Note Setting Access Permissions::. `--preserve-order' (See `--same-order'; *note Reading::.) `--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' Instructs `tar' to use SIZE bytes per record when accessing the archive. *Note Blocking Factor::. `--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 Reading::. `--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. `--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 `--show-omitted-dirs' Instructs `tar' to mention the directories it is skipping when operating on a `tar' archive. *Note show-omitted-dirs::. `--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::. `--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'. , summary `--suffix=SUFFIX' Alters the suffix `tar' uses when backing up files from the default `~'. *Note backup::. `--tape-length=NUM' `-L NUM' Specifies the length of tapes that `tar' is writing as being NUM x 1024 bytes long. *Note Using Multiple Tapes::. `--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' 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' 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'. `--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::. `--wildcards' Use wildcards when matching member names with patterns. *Note controlling pattern-matching::. `--wildcards-match-slash' Wildcards match `/'. *Note controlling pattern-matching::. ---------- 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. 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::. -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 creating, *note --no-same-owner::, when extracting -- *note --portability::. The later 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::. 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) 1.20 Copyright (C) 2008 Free Software Foundation, Inc. This is free software. You may redistribute copies of it under the terms of the GNU General Public License . 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 checking the spelling or meaning of some particular `tar' option, without resorting to this manual, for 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' option 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 `http://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. There is currently no `man' page for GNU `tar'. If you observe such a `man' page on the system you are running, either it does not belong to GNU `tar', or it has not been produced by GNU. Some package maintainers convert `tar --help' output to a man page, using `help2man'. In any case, please 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 if, one of this days, the `--version' would not output `tar (GNU paxutils) 3.2' 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. 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 cfv -', 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 if 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. 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 "meta-characters". The `%s' meta-character is replaced with the "type" of the checkpoint: `write' or `read' (or a corresponding translated version in locales other than POSIX). The `%u' meta-character 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 Aside from meta-character 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=\rHit %s checkpoint #%u" 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. 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 Finally, the `exec' action executes a given external program. For example: $ tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint This program is executed using `/bin/sh -c', with no additional arguments. Its exit code is ignored. It 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' The checkpoint number. `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. 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. 3.9 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. 4 GNU `tar' 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 cfT empty-archive.tar /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. 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. 4.2.1 The Five Advanced `tar' Operations ---------------------------------------- _(This message will disappear, once this node revised.)_ 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', `rock', 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' `-r' 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. 4.2.2 How to Add Files to Existing Archives: `--append' ------------------------------------------------------- _(This message will disappear, once this node revised.)_ 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 four 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.) ---------- Footnotes ---------- (1) Unless you give it `--keep-old-files' option, or the disk copy is newer than the the one in the archive and you invoke `tar' with `--keep-newer-files' option 4.2.2.1 Appending Files to an Archive ..................................... _(This message will disappear, once this node revised.)_ 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 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' wi