Almquist shell
Template:Short description {{#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 Almquist shell (also known as A Shell, ash and sh) is a lightweight Unix shell originally written by Kenneth Almquist in the late 1980s. Initially a clone of the System V.4 variant of the Bourne shell, it replaced the original Bourne shell in the BSD versions of Unix released in the early 1990s.
HistoryEdit
ash was first released via a posting to the Template:Mono Usenet news group, approved and moderated by Rich Salz on 30 May 1989. It was described as "a reimplementation of the System V shell [with] most features of that shell, plus some additions".<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Fast, small, and virtually compatibleTemplate:Citation needed with the POSIX standard's specification of the Unix shell, ash did not provide line editing or command history mechanisms, because Almquist felt that such functionality should be moved into the terminal driver. However, modern variants support it.
The following is extracted from the ash package information from Slackware v14:
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ash (Kenneth Almquist's ash shell)
A lightweight (92K) Bourne compatible shell. Great for machines with low memory, but does not provide all the extras of shells like bash, tcsh, and zsh. Runs most shell scripts compatible with the Bourne shell. Note that under Linux, most scripts seem to use at least some bash-specific syntax. The Slackware setup scripts are a notable exception, since ash is the shell used on the install disks. NetBSD uses ash as its /bin/sh.
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Myriad forks have been produced from the original ash release.<ref name=vars>{{#invoke:citation/CS1|citation
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}}</ref> These derivatives of ash are installed as the default shell (/bin/sh) on FreeBSD, NetBSD, DragonFly BSD, MINIX, and in some Linux distributions. MINIX 3.2 used the original ash version, whose test feature differed from POSIX.<ref>{{#invoke:citation/CS1|citation
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In 1997 Herbert Xu ported ash from NetBSD to Debian Linux. In September 2002, with release 0.4.1, this port was renamed to Dash (Debian Almquist shell). Xu's main priorities are POSIX conformance and slim implementation.<ref name=vars/>
Like its predecessor, Dash implements support for neither internationalization and localization nor multi-byte character encoding (both required in POSIX).Template:Citation needed Line editing and history support based on GNU Readline is optional (<syntaxhighlight lang="text" class="" style="" inline="1">--with-libedit</syntaxhighlight>).
Adoption in Debian and UbuntuEdit
Template:AnchorBecause of its slimness, Ubuntu decided to adopt Dash as the default /bin/sh<ref name="Debian">{{#invoke:citation/CS1|citation
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A result of the shift is that many shell scripts were found making use of Bash-specific functionalities ("bashisms") without properly declaring it in the shebang line.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The problem was first spotted in Ubuntu and the maintainers decided to make all the scripts comply with the POSIX standard. The changes were later upstreamed to Debian, which eventually adopted Dash as its default <syntaxhighlight lang="text" class="" style="" inline="1">/bin/sh</syntaxhighlight> too in Debian 6 (Squeeze), released in February 2011.<ref name="Debian"/> As a result, Debian policy was amended to allow script developers to assume a largely POSIX-compliant shell, save for the extensions merged into Dash for convenience (<syntaxhighlight lang="text" class="" style="" inline="1">local</syntaxhighlight>, <syntaxhighlight lang="text" class="" style="" inline="1">echo -n</syntaxhighlight>, <syntaxhighlight lang="text" class="" style="" inline="1">test -a / -o</syntaxhighlight>).<ref name=deb>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Man</ref> A similar transition has happened in Slackware Linux, although its version of <syntaxhighlight lang="text" class="" style="" inline="1">ash</syntaxhighlight> is only partially based on Dash.<ref name=vars/>
Embedded LinuxEdit
Ash (mainly the Dash fork) is also fairly popular in embedded Linux systems. Dash version 0.3.8-5 was incorporated into BusyBox, the catch-all executable often employed in this area. Modern BusyBox versions support additional Bash features which are enabled in modern distributions like Alpine Linux, Tiny Core Linux and Linux-based router firmware such as OpenWrt, Tomato and DD-WRT.