Almquist Shell: Difference between revisions

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{{implementation|UNIX Shell}}
 
{{implementation|UNIX Shell}}
'''Almquist Shell''' is a minimal implementation of an almost-[[POSIX]] shell, and also a replacement for [[compatible with::Bourne Shell]]. Almquist Shell has more features than. the original Bourne Shell, but fewer features than most other shells. (No arrays!) Almquist Shell only implements POSIX features, plus a few [[BSD]] traditions, like <code>local</code> variables in functions. Almquist Shell is the default shell, <code>/bin/sh</code>, of some systems. It 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, but since it lacks most non-POSIX features, it is helpful in validating that <tt>#!/bin/sh</tt> scripts are not dependent upon such features.
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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]]. Ash has more features than the original Bourne Shell, but fewer features than most other shells; for example, it lacks arrays. For the most part, it only implements POSIX features, but it does have a few traditional [[BSD]] add-ons, such as <code>local</code> variables in functions. Ash is the default shell, <code>/bin/sh</code>, of some systems.
   
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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>.
If a script works with Almquist Shell, it will probably also work with [[bash]], [[pdksh]] and [[zsh]]. Further, it will probably work with [[ksh93]] ''unless'' it uses <code>local</code>, which ksh93 lacks.
 
   
 
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.
 
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.

Latest revision as of 20:22, 20 September 2022

Almquist Shell is an implementation of UNIX Shell. Other implementations of UNIX Shell.

The Almquist Shell, a.k.a. ash, is a minimal implementation of an almost-POSIX shell, and also a replacement for the Bourne Shell. Ash has more features than the original Bourne Shell, but fewer features than most other shells; for example, it lacks arrays. For the most part, it only implements POSIX features, but it does have a few traditional BSD add-ons, such as local variables in functions. Ash is the default shell, /bin/sh, of some systems.

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 #!/bin/sh 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 typeset instead of local; unfortunately, while bash and zsh treat those commands as synonyms, ash in turn lacks typeset.

Almquist Shell filled the need for a free shell to replace Bourne Shell. Kenneth Almquist posted 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 /bin/sh, added features from POSIX, and put a Berkeley copyright on this shell.

Almquist variants[edit]

Ash has three major variants:

All three variants have similar features. Dash can run on GNU/Linux.

Ash is also the shell provided by BusyBox.

See also[edit]