shar

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.

This article is about the file format. For other uses, see Shar (disambiguation).

shar

Original author(s)	James Gosling
Developer(s)	Various open-source and commercial developers
Operating system	Unix, Unix-like, VMS, Windows
Type	Command

shar

Filename extension	.shar
Type of format	Archive format, shell script
Open format?	Yes[1]

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.

Details

While the shar format has the advantage of being plain text, it poses a risk due to being executable;[2] 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,[3] 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 similar formats

James Gosling is credited with writing the first version of the shar utility,[1] and also wrote an early example of the concept in the form of this simple shell script:[4][5][6]

# 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

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.[7] This was later maintained and extended by James A. Gray from Xerox,[8] and Andy Harper from King's College London.[9][10]

The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.[11]

See also

• List of Unix commands

References

1. "GNU 'shar' utilities". gno.org. Free Software Foundation. Retrieved 8 December 2019.
2. Apple (June 6, 1993). "Mac OS X shar(1) Man Page". Apple. Retrieved 2009-11-07.
3. "makeself "trap" command fix". Svn.icculus.org. 2000-11-20. Archived from the original on 2012-07-14. Retrieved 2011-08-30.
4. 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.
5. "shar: a blast from the past". James Gosling: on the Java Road. Archived from the original on March 27, 2017. Retrieved 26 March 2017.
6. An almost identical script, 'bundle', is described in "The UNIX Programming Environment", Kernighan and Pike, 1984, on page 97
7. Michael Bednarek (9 June 1987). "shar (sort of) for VMS". Newsgroup: comp.os.vms. Usenet: [e-mail]. Retrieved 2008-02-09.
8. Jim Gray (8 May 1988). "VMS_SHARE V6.0". Newsgroup: comp.os.vms. Usenet: 880508-073131-5929@Xerox. Retrieved 2008-02-09.
9. Andy Harper (6 July 1989). "VMS_SHARE version 7". Newsgroup: comp.os.vms. Usenet: [e-mail]. Retrieved 2008-02-09.
10. Andy Harper (5 July 1995). "Announcing VMS_SHARE 8.5". Newsgroup: vmsnet.sources.d. Usenet: [e-mail]. Retrieved 2008-02-09.
11. Native Win32 ports of some GNU utilities

External links

• shar(1) – Linux User Commands Manual
• Information about shar files (Carnegie Mellon)
• GNU sharutils