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6.3 Reading Names from a File

Instead of giving the names of files or archive members on the command line, you can put the names into a file, and then use the ‘--files-from=file-of-names’ (‘-T file-of-names’) option to tar. Give the name of the file which contains the list of files to include as the argument to ‘--files-from’. In the list, the file names should be separated by newlines. You will frequently use this option when you have generated the list of files to archive with the find utility.

--files-from=file-name
-T file-name

Get names to extract or create from file file-name.

If you give a single dash as a file name for ‘--files-from’, (i.e., you specify either --files-from=- or -T -), then the file names are read from standard input.

Unless you are running tar with ‘--create’, you can not use both --files-from=- and --file=- (-f -) in the same command.

Any number of ‘-T’ options can be given in the command line.

The following example shows how to use find to generate a list of files smaller than 400K in length and put that list into a file called ‘small-files’. You can then use the ‘-T’ option to tar to specify the files from that file, ‘small-files’, to create the archive ‘little.tgz’. (The ‘-z’ option to tar compresses the archive with gzip; see section Creating and Reading Compressed Archives for more information.)

 
$ find . -size -400 -print > small-files
$ tar -c -v -z -T small-files -f little.tgz

In the file list given by ‘-T’ option, any file name beginning with ‘-’ character is considered a tar option and is processed accordingly(14). For example, the common use of this feature is to change to another directory by specifying ‘-C’ option:

 
$ cat list
-C/etc
passwd
hosts
-C/lib
libc.a
$ tar -c -f foo.tar --files-from list

In this example, tar will first switch to ‘/etc’ directory and add files ‘passwd’ and ‘hosts’ to the archive. Then it will change to ‘/lib’ directory and will archive the file ‘libc.a’. Thus, the resulting archive ‘foo.tar’ will contain:

 
$ tar tf foo.tar
passwd
hosts
libc.a

If you happen to have a file whose name starts with ‘-’, precede it with ‘--add-file’ option to prevent it from being recognized as an option. For example: --add-file=--my-file.


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6.3.1 NUL-Terminated File Names

The ‘--null’ option causes ‘--files-from=file-of-names’ (‘-T file-of-names’) to read file names terminated by a NUL instead of a newline, so files whose names contain newlines can be archived using ‘--files-from’.

--null

Only consider NUL-terminated file names, instead of files that terminate in a newline.

--no-null

Undo the effect of any previous ‘--null’ option.

The ‘--null’ option is just like the one in GNU xargs and cpio, and is useful with the ‘-print0’ predicate of GNU find. In tar, ‘--null’ also disables special handling for file names that begin with dash.

This example shows how to use find to generate a list of files larger than 800K in length and put that list into a file called ‘long-files’. The ‘-print0’ option to find is just like ‘-print’, except that it separates files with a NUL rather than with a newline. You can then run tar with both the ‘--null’ and ‘-T’ options to specify that tar gets the files from that file, ‘long-files’, to create the archive ‘big.tgz’. The ‘--null’ option to tar will cause tar to recognize the NUL separator between files.

 
$ find . -size +800 -print0 > long-files
$ tar -c -v --null --files-from=long-files --file=big.tar

The ‘--no-null’ option can be used if you need to read both NUL-terminated and newline-terminated files on the same command line. For example, if ‘flist’ is a newline-terminated file, then the following command can be used to combine it with the above command:

 
$ find . -size +800 -print0 |
  tar -c -f big.tar --null -T - --no-null -T flist

This example uses short options for typographic reasons, to avoid very long lines.

GNU tar is tries to automatically detect NUL-terminated file lists, so in many cases it is safe to use them even without the ‘--null’ option. In this case tar will print a warning and continue reading such a file as if ‘--null’ were actually given:

 
$ find . -size +800 -print0 | tar -c -f big.tar -T -
tar: -: file name read contains nul character

The null terminator, however, remains in effect only for this particular file, any following ‘-T’ options will assume newline termination. Of course, the null autodetection applies to these eventual surplus ‘-T’ options as well.


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This document was generated by Sergey Poznyakoff on October, 20 2013 using texi2html 1.78.