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General archive commands

Table of Contents

cmd:tar & cmd:gzip

Usage

short form

tar -cvzf tfile files
tar -xvzf tfile

traditional form

And if your tar lacks support of the "z" flag, I strongly recommend using

gzip -d -c file.tar.gz | tar xvf -
tar cvf - files | gzip >file.tgz

instead of the two commands you suggest above --- both for performance and diskusage reasons.

for i in *gz ; do  gzip -d -c $i | tar xvf - ; done

Help

Main operation mode:
 -t, --list              list the contents of an archive
 -x, --extract, --get    extract files from an archive
 -c, --create            create a new archive
 -d, --diff, --compare   find differences between archive and file system
 -r, --append            append files to the end of an archive
 -u, --update            only append files newer than copy in archive
 -A, --catenate          append tar files to an archive

Operation modifiers:
 -k, --keep-old-files       don't overwrite existing files when extracting
 -U, --unlink-first         remove each file prior to extracting over it
     --recursive-unlink     empty hierarchies prior to extracting directory
 -S, --sparse               handle sparse files efficiently
 -O, --to-stdout            extract files to standard output

Device selection and switching:
 -f, --file=ARCHIVE             use archive file or device ARCHIVE

Archive format selection:
 -z, --gzip, --ungzip               filter the archive through gzip
 -Z, --compress, --uncompress       filter the archive through compress
     --use-compress-program=PROG    filter through PROG (must accept -d)

Local file selection:
 -h, --dereference            dump instead the files symlinks point to
     --no-recursion           avoid descending automatically in directories
 -N, --newer=DATE             only store files newer than DATE
     --newer-mtime            compare date and time when data changed only

Informative output:
 -v, --verbose         verbosely list files processed
 -w, --interactive     ask for confirmation for every action

Help

taken from the Debian User's Guide:

Large-Scale Copying

tar -cSpf - /usr/local | tar -xvSpf - -C /destination

The first tar command will archive the existing directory and pipe it to the second. The second command will unpack the archive into the location you specify with -C.

Update

Once you've performed a full backup of your files with tar, you can perform an incremental backup to keep the backup archive up-to-date.

Suppose you performed the full backup on Feb. 20, 2000, and a week later you wanted to add to the archive all the files that were created or altered since then. Use tar's -u option for this purpose. For example:

tar -uvf /home/bryan/backup/full-backup.tar /home/bryan

This command adds all the files that aren't present within the archive or that were altered since the creation of the backup archive (full-backup.tar).

Backing up your data with tar? Fine, but forget compression

It's possible to set up a system for backing up your data with the tar utility, but don't be tempted to use tar's built-in compression commands. Sure, you can create a tar archive that's compressed with gzip (to do so, type tar -czf followed by a space, the name of the archive you want to create, and the files you want to archive). But tar's update (-u) option won't work with compressed archives, so you won't be able to implement a backup system that makes periodic updates of only those files that have been created or changed since the last update.

Is this a horrendous flaw? Not really. Data security experts agree that compression shouldn't be used for backing up your data; compression increases the chance that the data will contain errors or become corrupted. For mission-critical data, it's not worth the risk.