Unfinished Drafts: Useful Utility: tar

This is another article that sat in the drafts folder for far too long- Last edited Feb 21st, 2006.

I fear writing about tar, and that is why I’m determined to finish it in this sitting, so it won’t fester and scare me off of this series. Why am I scared of writing about tar? Well, this is their flags list verbatim from the man page:

       [  --atime-preserve  ] [ -b, --blocking-factor N ] [ -B, --read-full-records ] [ --backup BACKUP-TYPE ] [ --block-com-
       press ] [ -C, --directory DIR ] [ --check-links ] [ --checkpoint ] [ -f, --file [HOSTNAME:]F ] [ -F,  --info-script  F
       --new-volume-script F ] [ --force-local   ] [ --format FORMAT ] [ -g, --listed-incremental F ] [ -G, --incremental ] [
       --group GROUP ] [ -h, --dereference ] [ --help ] [ -i, --ignore-zeros ] [ --ignore-case ] [ --ignore-failed-read  ]  [
       --index-file  FILE  ]  [ -j, --bzip2 ] [ -k, --keep-old-files ] [ -K, --starting-file F ] [ --keep-newer-files ] [ -l,
       --one-file-system ] [ -L, --tape-length N ] [ -m, --touch, --modification-time ] [ -M, --multi-volume ] [ --mode  PER-
       MISSIONS  ]  [  -N,  --after-date DATE, --newer DATE ] [ --newer-mtime DATE ] [ --no-anchored ] [ --no-ignore-case ] [
       --no-recursion ] [ --no-same-permissions ] [  --no-wildcards  ]  [  --no-wildcards-match-slash  ]  [  --null      ]  [
       --numeric-owner  ]  [  -o,  --old-archive, --portability, --no-same-owner ] [ -O, --to-stdout ] [ --occurrence NUM ] [
       --overwrite ] [ --overwrite-dir ] [ --owner USER ] [ -p, --same-permissions, --preserve-permissions ]  [  -P,  --abso-
       lute-names  ] [ --pax-option KEYWORD-LIST ] [ --posix ] [ --preserve ] [ -R, --block-number ] [ --record-size SIZE ] [
       --recursion ] [ --recursive-unlink ] [ --remove-files ] [ --rmt-command CMD ] [ --rsh-command  CMD  ]  [  -s,  --same-
       order, --preserve-order ] [ -S, --sparse ] [ --same-owner ] [ --show-defaults ] [ --show-omitted-dirs ] [ --strip-com-
       ponents NUMBER, --strip-path NUMBER (1) ] [ --suffix SUFFIX ] [ -T, --files-from F ] [ --totals   ]  [  -U,  --unlink-
       first ] [ --use-compress-program PROG ] [ --utc ] [ -v, --verbose ] [ -V, --label NAME ] [ --version  ] [ --volno-file
       F ] [ -w, --interactive, --confirmation ] [ -W, --verify ] [ --wildcards ] [  --wildcards-match-slash  ]  [  --exclude
       PATTERN  ]  [  -X,  --exclude-from  FILE  ]  [  -Z,  --compress,  --uncompress  ] [ -z, --gzip, --gunzip, --ungzip ] [
       -[0-7][lmh] ]

So it’s a bit overwhelming. The good news is there are two common uses for tar- creating tarballs and opening tarballs. This will be a majority of your interaction with it. You get all sorts of fun options with tar, such as using different compression libraries, but it’s still pretty straight forward.

Simple Archive

Tar produces tarballs, which in its simplest form is a bunch of data files run together into a larger file. in the following instance, -c means create, and -f means “create the following as a file called foo.tar”

tar -cf foo.tar bar/

This takes the bar directory and throws it all into a single file called foo.tar. Apart from some binary mojo to mark the separators between files, it’s almost as it all of the files were pasted end-to-end inside another file. if foo.tar is copied to another machine or place, you could untar the file with the following command:

tar -xf foo.tar

Again you see the -f flag, but the -c flag has been replaced by the extract flag, -x. This will create a directory called bar/ which will contain the contents identical to the original.

Compressing Archives

You also have the option of compressing tarballs in the process of creating them. There are three types of compression built into the version of tar I’m using: -Z, which uses the compress utility (ancient?); -z which uses gzip (old standard); and -j, which uses b2zip, which is good for compressing binaries (appears to be the new standard).

When creating a tarball that is compressed, it’s generally expected that you label it as such by appending the type to the filename, for example:

tar -cZf foo1.tar.Z bar1/
tar -czf foo2.tar.gz bar2/
tar -cjf foo3.tar.bz2 bar3/

Unless you have a specific reason, you’ll probably want to use bz2. You’ll probably never deal with a tar.Z file, but if you do, you’ll know how to deal with it. To uncompress these puppies, switch out the -c flag for the -x flag like we did in the previous example.

tar -xZf foo1.tar.Z
tar -xzf foo2.tar.gz
tar -xjf foo3.tar.bz2

One last option you may want to look at is -v. It will show you files as they’re being processed, and can be good for troubleshooting.