Interaction with OpenBSD's default shell, pdksh
|Original author(s)||David Korn|
u+ / August 1, 2012
ksh) is a Unix shell which was developed by David Korn at Bell Labs in the early 1980s and announced at USENIX on July 14, 1983. The initial development was based on Bourne shell source code. Other early contributors were Bell Labs developers Mike Veach and Pat Sullivan, who wrote the Emacs and vi-style line editing modes' code, respectively. KornShell is backward-compatible with the Bourne shell and includes many features of the C shell, inspired by the requests of Bell Labs users.
KornShell complies with POSIX.2, Shell and Utilities, Command Interpreter (IEEE Std 1003.2-1992.) Major differences between KornShell and the traditional Bourne shell include:
- Job control, command aliasing, and command history designed after the corresponding C shell features. Job control was added to the Bourne Shell in 1989.
- A choice of three command line editing styles based on vi, Emacs, and Gosling Emacs.
- Associative arrays and built-in floating point arithmetic operations (only available in the ksh93 version of KornShell).
- Dynamic extensibility of built-in commands (as of ksh93).
KornShell was originally proprietary software. In 2000 the source code was released under a license particular to AT&T, but since the 93q release in early 2005 it has been licensed under the Eclipse Public License. KornShell is available as part of the AT&T Software Technology (AST) Open Source Software Collection. As KornShell was initially only available through a proprietary license from AT&T, a number of free and open source alternatives were created. These include pdksh, mksh, bash, and zsh.
The functionality of the original KornShell, ksh88, was used as a basis for the standard POSIX.2, Shell and Utilities, Command Interpreter (IEEE Std 1003.2-1992.)
As "Desktop KornShell" (dtksh), ksh93 is distributed as part of the Common Desktop Environment. This version also provides shell-level mappings for Motif widgets. It was intended as a competitor to Tcl/Tk.
UnixWare 7 includes both ksh88 and ksh93. The default Korn shell is ksh93, which is supplied as /usr/bin/ksh, and the older version is available as /usr/bin/ksh88. UnixWare also includes dtksh when CDE is installed.
The ksh93 distribution underwent a less stable fate after the authors left AT&T around 2012 at stable version ksh93u+. The authors continued working on a ksh93v- beta branch until around 2014, when a few community developers essentially "took over" and kept working to produce a heavily refactored "ksh2020". In March 2020, AT&T decided to roll back the community changes, stash them in a branch, and restart from ksh93u+, as the changes were too broad and too ksh-focused for the company to absorb into a project in maintenance mode. Debian offers ksh2020 in its testing version.
There are several software products related to KornShell:
- dtksh – a fork of ksh93 included as part of CDE.
- tksh – a fork of ksh93 that provides access to the Tk widget toolkit.
- oksh – a port of OpenBSD's flavour of KornShell, intended to be maximally portable across operating systems. It was used as the default shell in DeLi Linux 7.2.
- mksh – a free implementation of the KornShell language, forked from pdksh. It was originally developed for MirOS BSD and is licensed under permissive (though not public domain) terms; specifically, the MirOS Licence. In addition to its usage on BSD, this variant has replaced pdksh on Debian, and is the default shell on Android.
- SKsh – an AmigaOS flavour that provides several Amiga-specific features, such as ARexx interoperability.
- MKS Inc.'s MKS Korn shell – a proprietary implementation of the KornShell language from Microsoft Windows Services for UNIX (SFU) up to version 2.0; according to David Korn, the MKS Korn shell was not fully compatible with KornShell in 1998. In SFU version 3.0 Microsoft replaced the MKS Korn shell with a new POSIX.2-compliant shell as part of Interix.
- KornShell is included in UWIN, a Unix compatibility package by David Korn.
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Instead of inventing a new script language, we built a form entry system by modifying the Bourne shell, adding built-in commands as necessary.
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