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Concatenating Archives

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Rather than adding individual files onto the end of an archive, it may be more convenient to add archives themselves onto the end of an archive. While it may seem intuitive to use cat, the utility for adding files together, for this purpose, archives created by tar incorporate an end of file marker which must be removed if the concatenated archives are to be read properly as one archive

FIXME: xref Ignore zeros.

In earlier examples you created an archive file, `music', in your home directory. You have, however, since changed the contents of the `practice' directory which was stored in that archive. `records', the archive file in the `practice' directory, has recently been updated, and contains a current version of the files in `practice'. Rather than update the contents of `music', let's add `records' to it.

• Change into the home directory (`cd ..')
• Invoke tar, and specify the operation to add archives to the end of another archive---`--concatenate' (`-A').
• Specify the name of the archive file to be added to---`--file=archive-name' (`-f archive-name').
• Specify the file name arguments, which are, unusually, the names of archive files. Remember to include the directory name in the file name, if the archive file is not in your working directory.

% cd ..
% tar --concatenate --file=music practice/records

Rather than list the new contents of `music', let's extract all the files and see what happens.

To concatenate archive files, use the `--concatenate' (`-A') option. This operation adds other archives to the end of an archive. While it may seem intuitive to concatenate archives using cat, the utility for adding files together, archive files which have been "catted" together cannot be read properly by tar. Archive files incorporate an end of file marker--if archives are concatenated using cat, this marker will appear before the end of the new archive. This will interfere with operations on that archive.

FIXME: xref ignore-zeros

In earlier examples, you stored the `~/practice' directory in an archive file, `~/music'. If you have been following the examples, you have since changed the contents of the `~/practice' directory. There is a current version of the files in the `practice' directory, however, stored in the archive file `~/practice/records'.

To store current versions of the files in `practice' in the archive file `music', you can use `--concatenate' (`-A') to add the archive file `~/practice/records' to `music'. First, make sure you are in your home directory (`cd ~'). Then:

• Invoke tar, and specify the `--concatenate' (`-A') operation.

• Specify the archive file to be added to---`--file=archive-name' (`-f archive-name').

• Specify the archives to be added, using file name arguments. In this case, the file name arguments are, unusually, the names of archive files. (Remember to include the path in the archive name, if the archive file is not in your working directory.)

% cd ~
% tar --concatenate --file=music practice/records

If you now list the contents of the `music', you see it now contains the archive members of `practice/records':

%tar --list --file=music
blues
folk
jazz
rock
blues
practice/blues
practice/folk
practice/jazz
practice/rock
practice/blues
practice/classical

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