Shar (file format)
Template:Short description Template:Lowercase {{#invoke:Infobox|infobox}}Template:Template other{{#invoke:Check for unknown parameters | check | showblankpositional=1 | unknown = Template:Main other | preview = Page using Template:Infobox software with unknown parameter "_VALUE_"|ignoreblank=y | AsOf | author | background | bodystyle | caption | collapsetext | collapsible | developer | discontinued | engine | engines | genre | included with | language | language count | language footnote | latest preview date | latest preview version | latest release date | latest release version | latest_preview_date | latest_preview_version | latest_release_date | latest_release_version | licence | license | logo | logo alt | logo caption | logo upright | logo size | logo title | logo_alt | logo_caption | logo_upright | logo_size | logo_title | middleware | module | name | operating system | operating_system | other_names | platform | programming language | programming_language | released | replaced_by | replaces | repo | screenshot | screenshot alt | screenshot upright | screenshot size | screenshot title | screenshot_alt | screenshot_upright | screenshot_size | screenshot_title | service_name | size | standard | title | ver layout | website | qid }}Template:Main other Template:Infobox file format
In the Unix operating system, shar (from "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.
shar files are also sometimes called "sharchives" (from "/bin/sh archive").<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
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.
DetailsEdit
While the shar format has the advantage of being plain text, it poses a risk due to being executable;<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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,<ref>{{#invoke:citation/CS1|citation
|CitationClass=web
}}</ref> 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 variantsEdit
James Gosling is credited with writing the first version of the shar utility in 1982,<ref name=gnu>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>Template:Rp and also wrote an early example (allegedly 1978-79) of the concept in the form of this simple shell script:<ref>Template:Cite newsgroup</ref><ref name=jag>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>An almost identical script, 'bundle', is described in "The UNIX Programming Environment", Kernighan and Pike, 1984, on page 97</ref>
<syntaxhighlight lang="bash">
- 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 </syntaxhighlight>
The following variants of shar are known:<ref name="Dickey">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
- shar 1.x (1982) by Gosling. Public domain shell script.
- Current FreeBSD shar. 3-clause BSD license, shell script. Adds md5sum.
- 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.
GNU <syntaxhighlight lang="text" class="" style="" inline="1">shar</syntaxhighlight> 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.<ref>Native Win32 ports of some GNU utilities</ref>
Similar formatsEdit
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.<ref>Template:Cite newsgroup</ref> This was later maintained and extended by James A. Gray from Xerox,<ref>Template:Cite newsgroup</ref> and Andy Harper from King's College London.<ref>Template:Cite newsgroup</ref><ref>Template:Cite newsgroup</ref>
makeself (2001–) is a shell script that generates self-extracting tarballs (<syntaxhighlight lang="text" class="" style="" inline="1">*.run</syntaxhighlight>, <syntaxhighlight lang="text" class="" style="" inline="1">application/x-makeself</syntaxhighlight>) 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 21st century among software vendors seeking to package Linux software.<ref name=makeself>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>