the -a flag causes tar to automatically pick the right compressor to filter the archive through, based on the file extension. e.g.

"tar -xaf archive.tar.xz" is equivalent to "tar -xJf archive.tar.xz"

"tar -xaf archive.tar.gz" is equivalent to "tar -xzf archive.tar.gz"

No need to remember -z is gzip, -j is bzip2, -Z is .Z, -J is xz, and so on :)

Simple Compressed Backup of the /etc

Linux compatible

Sometimes you might need to have two copies of data that is in tar. You might unpack, and then copy, but if IO is slow, you might lower it by automatically writing it twice (or more times)

The result of this command is a tar with all files that have been modified/added since revision 1792 until HEAD. This command is super useful for incremental releases.

Useful when you have multiple files or binary files that you need to transfer to a different host and scp or the like is unavailable.

To unpack on the destination host copy paste output using the opposite order:

openssl enc -d -base64 | gunzip | tar -x

Terminate openssl input using ^d

Note: gzip is outside of tar because using -z in tar produces lots of extra padding.

Create a encrypted tar.gz file from a directory on the fly. The encryption is done by GPG with a public key. The resulting filename is tagged with the date of creation. Very usefull for encrypted snapshots of folders.

`tar xfzO` extracts to STDOUT which got redirected directly to mysql. Really helpful, when your hard drive can't fit two copies of non-compressed database :)

Backups $DIR_TO_BACKUP into tape, creating on the fly a MD5SUM file of the backup.

Then rewinds one record on tape and checks if it's well written.

tar does not have a -mtime option as find. tar appends all the file to an existing tar file.

This will uncompress the file while it's being downloaded which makes it much faster

A quick find command to identify all TAR files in a given path, extract a list of files contained within the tar, then search for a given string in the filelist. Returns to the user as a list of TAR files found (enclosed in []) followed by any matching files that exist in that archive. TAR can easily be swapped for JAR if required.

in fact, I want to know, how to only get the modified files.

Source:

http://unix.derkeiler.com/Newsgroups/comp.unix.shell/2008-04/msg00068.html

If you want to decompress the files from an archive to current directory by stripping all directory paths, use --transform option to strip path information. Unfortunately, --strip-components option is good if the target files have same and constant depth of folders.

The idea was taken from http://www.unix.com/solaris/145941-how-extract-files-tar-file-without-creating-directories.html

This is freaking sweet!!! Here is the full alias, (I didn't want to cause display problems on commandlinefu.com's homepage):

Creates a .tgz archive of whatever directory it is run from, in the background, detached from current shell so if you logout it will still complete. Also, you can run this as many times as you want, if the archive .tgz already exists, it just moves it to a numbered backup '--backup=numbered'. The coolest part of this is the transformation performed by tar and sed so that the archive file names are automatically created, and when you extract the archive file it is completely safe thanks to the transform command.

If you archive lets say /home/tombdigger/new-stuff-to-backup/ it will create the archive /home/#home#tombdigger#new-stuff-to-backup#-2010-11-18.tgz Then when you extract it, like tar -xvzf #home#tombdigger#new-stuff-to-backup#-2010-11-18.tgz instead of overwriting an existing /home/tombdigger/new-stuff-to-backup/ directory, it will extract to /home/tombdigger/new-stuff-to-backup.2010-11-18/

Basically, the tar archive filename is the PWD with all '/' replaced with '#', and the date is appended to the name so that multiple archives are easily managed. This example saves all archives to your $HOME/archive-name.tgz, but I have a $BKDIR variable with my backup location for each shell user, so I just replaced HOME with BKDIR in the alias.

So when I ran this in /opt/askapache/SOURCE/lockfile-progs-0.1.11/ the archive was created at /askapache-bk/#opt#askapache#SOURCE#lockfile-progs-0.1.11#-2010-11-18.tgz

Upon completion, uses the universal logger tool to output its completion to syslog and stderr (printed to your terminal), just remove that part if you don't want it, or just remove the '-s ' option from logger to keep the logs only in syslog and not on your terminal.

Here's how my syslog server recorded this..

2010-11-18T00:44:13-05:00 gravedigger.askapache.com (127.0.0.5) [user] [notice] (logger:) Tarred /opt/askapache/SOURCE/lockfile-progs-0.1.11 to /askapache-bk/tarred/#opt#SOURCE#lockfile-progs-0.1.11#-2010-11-18.tgz in 4 seconds

Caveats

Really this is very robust and foolproof, the only issues I ever have with it (I've been using this for years on my web servers) is if you run it in a directory and then a file changes in that directory, you get a warning message and your archive might have a problem for the changed file. This happens when running this in a logs directory, a temp dir, etc.. That's the only issue I've ever had, really nothing more than a heads up.

Advanced:

This is a simple alias, and very useful as it works on basically every linux box with semi-current tar and GNU coreutils, bash, and sed.. But if you want to customize it or pass parameters (like a dir to backup instead of pwd), check out this function I use.. this is what I created the alias from BTW, replacing my aa_status function with logger, and adding $SECONDS runtime instead of using tar's --totals

{

local GZIP='--fast' PWD=${1:-`pwd`} F=$(date +${BKDIR}/%m-%d-%g-%H%M-`sed -u 's/[\/\ ]/#/g'

[[ ! -r "$PWD" ]] && echo "Bad permissions for $PWD" 1>&2 && return 2;

( ( tar --totals --ignore-failed-read --transform "s@^${PWD%/*}@`date +${PWD%/*}.%m-%d-%g`@S" -czPf $F $PWD && aa_status "Completed Tarp of $PWD to $F" ) & )

}

#From my .bash_profile http://www.askapache.com/linux-unix/bash_profile-functions-advanced-shell.html

The J option is a recent addition to GNU tar. The xz compression utility is required as well.

Same, but count of signs is little less :) .

A *.tar.gz file needs to be unzipped & then untarred. Previously I might have unzipped first with

and then untarred the result with

(Options are extract, verbose, file)

Using the -z (decompress) option on tar avoids the use of gzip (or gunzip) first.

Additionally the -C option will specify the directory to extract to.