Korn Shell
Korn Shell, or ksh, is the creation of David Korn at AT&T. This shell combines Bourne Shell syntax with a command-line editor, command history, tilde expansion, arithmetic expressions, arrays, co-processes and several more features. Korn Shell has influenced many later shells; Bourne Again SHell and Z Shell clone several features, and the X/Open and POSIX standards take a few features from Korn Shell. David Korn continues to maintain ksh93, the original implementation.
AT&T freed ksh93 during 2000, using an open-source license. For many years before that, the original Korn Shell was not free; it was only part of AT&T System V and some commercial Unix variants. Therefore, ksh in some systems is not David Korn's shell, but is some other shell, perhaps pdksh or mksh.
Which Korn Shell do I have?
Start ksh and run
$ echo $KSH_VERSION
- If the output looks like
Version JM 93u 2011-02-08, then you have ksh93.- Version AJM 93u+ 2012-08-01
- If the output looks like
@(#)PD KSH v5.2.14 99/07/13.2, then you have pdksh. - If the output looks like
@(#)MIRBSD KSH R49 2014/01/11, then you have mksh. - A zsh invoked as ksh sets ZSH_VERSION, not KSH_VERSION.