Almquist Shell: Difference between revisions
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{{implementation|UNIX Shell}}
The '''Almquist Shell''', a.k.a. <tt>ash</tt>, is a minimal implementation of an almost-[[POSIX]] shell, and also a replacement for the [[compatible with::Bourne Shell]].
The Almquist Shell does not have any of the internationalization/localization or multi-byte character encoding support required by the POSIX standard, so it is not technically a POSIX-compliant shell. Nonetheless, since it lacks most non-POSIX features, it is helpful in validating that <tt>#!/bin/sh</tt> scripts are not dependent upon such features. In general, if a script works with Almquist Shell, it will probably also work with other popular Bourne-compatible shells, such as the [[Bourne Again SHell]] and [[Z Shell]]. It may not work with the [[Korn Shell]], which uses <tt>typeset</tt> instead of <tt>local</tt>; unfortunately, while bash and zsh treat those commands as synonyms, ash in turn lacks <tt>typeset</tt>.
Almquist Shell filled the need for a free shell to replace Bourne Shell. Kenneth Almquist posted [http://groups.google.com/group/comp.sources.unix/msg/2774e7653a8e6274 the first version of Ash] to Usenet group comp.sources.unix at 30 May 1989. It was a clone of SVR3 Bourne Shell. [[BSD]] used Ash for <code>/bin/sh</code>, added features from POSIX, and put a Berkeley copyright on this shell.
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Ash has three major variants:
* [[Debian Almquist Shell]] (Dash), which adds support for
* [http://svnweb.freebsd.org/base/head/bin/sh/ FreeBSD /bin/sh]
* [http://cvsweb.netbsd.org/bsdweb.cgi/src/bin/sh/?only_with_tag=MAIN NetBSD /bin/sh]
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