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tar

tb2

tgz

Name origin: Tape ARchive.

The tar format is specified by POSIX 7 together with the pax utility: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92

The tar is a GNU implementation, and is not specified by POSIX.

tar only turns a dir into file, but does no compression.

It is a popular option to transform directories in to files in Nix systems, as the format natively stores and preserves ext filesystem metadata such as:

  • ownership
  • permissions
  • symlinks
  • timestamps

Since tar offers no compression, it is often coupled with gz and bz2: those are files compressors.

tar end compressions are used so commonly together that shorthand extensions exist for them:

  • tgz == tar.gz
  • txz == tar.xz
  • tb2 == tbz == tar.bz2

General GNU interface:

  • single char options don't start with hyphen
  • every single letter option has a corresponding double hyphen multi char version

Create tar:

tar vcf "$F".tar "$F"
tar vczf "$F".tgz "$F"
tar vcjf "$F".tbz "$F"
tar vcJf "$F".txz "$F"
  • c: create
  • f: set output file to next argument. If not given, outputs to stdout.
  • z: gzip
  • j: bzip2
  • v: verbose

If the output file exists, it is overwritten.

Create from tar with multiple files:

tar vcf a.tar f1 f2

r: append file to existing tar, or create new tar:

tar rcf a.tar f

Extract:

tar vxf "$F".tar
tar vxzf "$F".tgz
tar vxjf "$F".tbz

Keep hardlinks

Does not work if the file has any hard links, probably because that would not reduce memory usage as it breaks the hardlink. AKA: tries to be too smart and annoys us to hell!

Workaround: keep the original on the operations: http://unix.stackexchange.com/questions/46786/how-to-tell-gzip-to-keep-original-file

Workarounds: -c outputs to stdout:

gzip -c a > a.gz

Read input from stdin:

gzip < a > a.gz

And finally, gzip 1.6 (2013) has the -k, --keep option:

gzip -k a
gzip -kr .