|Original author(s)||James Gosling|
|Developer(s)||Various open-source and commercial developers|
|Operating system||Unix, Unix-like, VMS, Windows|
|Type of format||Archive format, shell script|
In the Unix operating system, shar (an abbreviation of shell archive) is an archive format created with the Unix
shar utility. A shar file is a type of self-extracting archive, because it is a valid shell script, and executing it will recreate the files. To extract the files, only the standard Unix Bourne shell sh is usually required.
Note that the shar command is not specified by the Single Unix Specification, so it is not formally a component of Unix, but a legacy utility.
While the shar format has the advantage of being plain text, it poses a risk due to being executable; for this reason the older and more general tar file format is usually preferred even for transferring text files. GNU provides its own version of shar in the GNU Sharutils collection.
unshar programs have been written for other operating systems but are not always reliable; shar files are shell scripts and can theoretically do anything that a shell script can do (including using incompatible features of enhanced or workalike shells), limiting their utility outside the Unix world.
The drawback of self-extracting shell scripts (any kind, not just shar) is that they may rely on a particular implementation of programs; shell archives created with older versions of makeself, for example, the original Unreal Tournament for Linux installer, fails to run on bash 3.x due to a change in how missing arguments to
trap built-in command are handled.
History and variants
James Gosling is credited with writing the first version of the shar utility in 1982,: §1 and also wrote an early example (allegedly 1978-79) of the concept in the form of this simple shell script:
# shar -- Shell archiver AR=$1 shift for i do echo a - $i echo "echo x - $i" >>$AR echo "cat >$i <<'!Funky!Stuff!'" >>$AR cat $i >>$AR echo "!Funky!Stuff!" >>$AR done
The following variants of shar are known:
- shar 1.x (1982) by Gosling. Public domain shell script.
- shar2 or xshar (1988) by William Davidsen. Public domain, C program.
- cshar (1984) by Michael A. Thompson and Mark Smith, now lost to bitrot. C program.
- cshar (1988) by Rich Salz, C program. Likely influenced shar 3.49.
- ccshar (1996), a modification to output a csh script instead. Rarely used on Usenet.
A version of the same concept, but for the VMS operating system, was written in 1987 by Michael Bednarek from The Melbourne Institute of Applied Economic and Social Research as a DCL script, VMS_SHAR.COM. This was later maintained and extended by James A. Gray from Xerox, and Andy Harper from King's College London.
makeself (2001–) is a shell script that generates self-extracting tarballs (
application/x-makeself) using the same shell script header technique. Using tar precludes makeself from being used in plain text directly, but the better compression and other functionalities has made it more popular in the 21th century among software vendors seeking to package Linux software.
- "GNU 'shar' utilities". gnu.org. Free Software Foundation. Retrieved 8 December 2019.
- Apple (June 6, 1993). "Mac OS X shar(1) Man Page". Apple. Retrieved 2009-11-07.
- "makeself "trap" command fix". Svn.icculus.org. 2000-11-20. Archived from the original on 2012-07-14. Retrieved 2011-08-30.
- uw-beave!jim (April 2, 1983). "Re: program to separate xlisp distribution files". Newsgroup: net.sources. message-id:bnews.uw-beave.451. Retrieved March 27, 2017.
- "shar: a blast from the past". James Gosling: on the Java Road. Archived from the original on March 27, 2017. Retrieved 26 March 2017.
- An almost identical script, 'bundle', is described in "The UNIX Programming Environment", Kernighan and Pike, 1984, on page 97
- Dickey, Thomas E. "Comments on Shar/Utils". invisible-island.net.
- Native Win32 ports of some GNU utilities
- Michael Bednarek (9 June 1987). "shar (sort of) for VMS". Newsgroup: comp.os.vms. Usenet: 1261@murdu.OZ. Retrieved 2008-02-09.
- Jim Gray (8 May 1988). "VMS_SHARE V6.0". Newsgroup: comp.os.vms. Usenet: 880508-073131-5929@Xerox. Retrieved 2008-02-09.
- Andy Harper (6 July 1989). "VMS_SHARE version 7". Newsgroup: comp.os.vms. Usenet: 8907061417.AA16991@ucbvax.Berkeley.EDU. Retrieved 2008-02-09.
- Andy Harper (5 July 1995). "Announcing VMS_SHARE 8.5". Newsgroup: vmsnet.sources.d. Usenet: 1994Jul5.email@example.com. Retrieved 2008-02-09.
- "makeself - Make self-extractable archives on Unix".