| Paradigm(s) | imperative, pipeline |
|---|---|
| Appeared in | 1983[1][2] |
| Designed by | David Korn |
| Developer | AT&T Bell Laboratories |
| Major implementations | ksh88, ksh93, dtksh, tksh, pdksh, mksh, SKsh, MKS Korn shell |
| Influenced by | Bourne shell, C shell |
| Influenced | zsh, bash, Windows PowerShell |
| OS | Cross-platform |
| License | Common Public License (AT&T ksh), MirOS Licence (mksh), mostly Public Domain with some GPL (pdksh) |
| Stable release | ksh93u / February 8, 2011[3] |
|---|
| Stable release | R40[4] / June 12, 2011[5] |
|---|
| Stable release | 0.4.1 / August 28, 2010[6] |
|---|
The Korn shell (ksh) is a Unix shell which was developed by David Korn (AT&T Bell Laboratories) in the early 1980s and announced at USENIX on July 14, 1983.[1][2] Other early contributors were AT&T Bell Labs developers Mike Veach, who wrote the emacs code, and Pat Sullivan, who wrote the vi code.[7] ksh is backwards-compatible with the Bourne shell and includes many features of the C shell as well, such as a command history, which was inspired by the requests of Bell Labs users.
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The main advantage of ksh over the traditional Unix shell is in its use as a programming language. Since its conception, several features were gradually added, while maintaining strong backwards compatibility with the Bourne shell.
The ksh93 version supports associative arrays and built-in floating point arithmetic.
For interactive use, ksh provides the ability to edit the command line in a WYSIWYG fashion, by hitting the appropriate cursor-up or previous-line key-sequence to recall a previous command, and then edit the command as if the users were in edit line mode. Three modes are available, compatible with vi, emacs and XEmacs.
ksh aims to respect the Shell Language Standard (POSIX 1003.2 "Shell and Utilities Language Committee").
Until 2000, Korn Shell remained AT&T's proprietary software. Since then it has been open source software, originally under a license particular to AT&T but, since the 93q release in early 2005, it has been licensed under the Common Public License. Korn Shell is available as part of the AT&T Software Technology (AST) Open Source Software Collection. As ksh was initially only available through a proprietary license from AT&T, a number of free and open source alternatives were created. These include the public domain pdksh and its actively developed successor mksh, the Free Software Foundation's Bourne-Again-Shell bash, and zsh.
The functionality of the original Korn Shell (known as ksh88 from the year of its introduction) was used as a basis for the POSIX shell standard.
Although the ksh93 version added many improvements (associative arrays, floating point arithmetic, etc.), some vendors still ship their own version of the older ksh88 as /bin/ksh, sometimes with extensions. ksh93 is still maintained by its author. Releases of ksh93 are versioned by appending a letter to the name; the current version is ksh93u (released 2011-02-08); the previous version was ksh93t+ (released 2009-05-01) following ksh93t (released 2008-06-24). Some intermediate bug-fix versions are released without changes to this version string.[8]
As "Desktop KornShell", dtksh, the ksh93 was distributed as part of the Common Desktop Environment with several Unix systems, including Solaris, AIX, and HP-UX.[9] This version also provide shell-level mappings for Motif widgets. It was intended as competitor to tcl/tk.[10]
There are also two modified versions of ksh93 which add features for manipulating the graphical user interface: dtksh which is part of CDE and tksh which provides access to the Tk widget toolkit.
mksh (MirBSD Korn Shell) is an actively developed, BSDish-licensed, flavour of ksh. It is a direct descendant from the OpenBSD's /bin/ksh and heir of pdksh. mksh development focuses on code portability, security fixes, UTF-8 support, and tries to avoid feature creep.[11] It will, however, track POSIX closely and implement many ksh93 and some bash or zsh extensions. It is available for many unix-like operating systems[12] and is a default shell of MirOS BSD, FreeWRT, MidnightBSD, Android-x86, Android 3.0 (Honeycomb) and possibly Android 4 (Ice Cream Sandwich).
oksh is a port of OpenBSD's /bin/ksh to GNU/Linux which only contains enough modifications so that the code can compile under a GNU/Linux system. It is used as the default shell in DeLi Linux.
SKsh is an AmigaOS version, that offers several Amiga-specific features such as ARexx interoperability.
MKS Inc.'s MKS Korn shell is another proprietary ksh reimplementation. It was included with Microsoft's Services for Unix (SFU) up to version 2.0. According to David Korn, the MKS Korn shell was not fully compatible with his own Korn shell implementation in 1998.[13][14]
With the introduction of SFU Version 3.0, Microsoft has replaced the MKS Korn shell with a new and fully POSIX compliant Korn shell as part of the new native Interix subsystem technology.[15] It is supported on Windows NT 4.0 SP6a+, Windows 2000, Windows XP Professional and Windows Server 2003. It is also available in the Subsystem for UNIX-based Applications (SUA) of Windows Vista and 7 Enterprise and Ultimate Editions only and Windows Server 2008.[16][17][18] It is the default shell (/bin/sh) for SUA.[19] The Korn shell is also included in UWIN, a separate Unix compatibility package created by Korn himself;[20] however, UWIN only explicitly support versions of Windows up to XP, included.
The original Korn shell (ksh88) is the default shell on AIX since AIX version 4.[21][22] with ksh93 available separately.[23]
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