- This article is about the electronic archive format. For physical tape archives, see Magnetic tape or Punched tape.
Tape Archive (tar) is a traditional UNIX archive format, defined in POSIX.1-1988 and later POSIX.1-2001. Its original purpose was to archive files on backup tapes. Archived data in the tar format is sometimes referred to as a "tarball".
While tar itself does not offer any compression, it's frequently used together with a stream compression format such as gzip, bzip2, or XZ to provide file archiving plus compression. Most modern implementations of tar, present in UNIX/Linux systems, offer built-in support for this combined operation by using a modifier such as z (gzip) or j (bzip2). When extracting files, the compression format can sometimes be detected and handled automatically.
Files compressed this way should have a dual file extension such as .tar.gz or tar.bz2. Sometimes the .tgz extension is used in place of .tar.gz. Rarely, other shortened extensions are used:
- .tbz instead of .tar.bz2 (bzip2)
- .txz instead of .tar.xz (XZ)
- .tlz instead of .tar.lz (Lzip) or .tar.lzma (LZMA_Alone)
- .taz instead of .tar.Z (compress) (or possibly some other compressed format)
- .tz instead of .tar.Z (compress) (or possibly some other compressed format)
There exist some variants to the TAR archive format. The original POSIX.1-1988 TAR format had limitations on the type of files it could contain and the length of filenames. That's why the USTAR format was later developed and standardized as POSIX IEEE P1003.1. Jörg Schilling has collected some information about the different implementations; see the references section. There's also an old version (often referred to as "non-ANSI Tar" or simply "old Tar") which both GNU Tar and STar can read and write.
Disk Archiver (DAR) was intended by its authors as a replacement for TAR, supporting file compression among other features.
Compressing two files into a .tar.gz archive:
tar cvzf output.tar.gz inputfile1 inputfile2
Extracting a .tar.gz archive to the current directory:
tar xvzf output.tar.gz
With some versions of tar, the "
z" flag can be omitted when extracting ("
tar xvf ...").
- Linux man page for tar
- FreeBSD man page giving format info
- star man page by Jörg Schilling
- Chart of TAR format