Shell Scripting: Expert Recipes for Linux, Bash, and More

The KornShell

The Kornshell (ksh) was written by David Korn in 1983. It is a very popular shell for scripting as well as interactive use, particularly on proprietary Unices. Like bash and dash, it is backward-compatible with the Bourne shell but adds new features and syntax. Ksh introduced cursor-key navigation of the shell history, as well as providing arrays and floating-point math. For a long time, ksh was proprietary Unix software of AT&T, so pdksh (now mksh, http://mirbsd.de/mksh) is a Free Software equivalent to ksh93. After ksh93 was released under IBM’s Common Public License in 2005, most GNU/Linux distributions included ksh93 instead of pdksh or mksh, as did OpenSolaris. As a result, whenever you find ksh on a recent system, it is likely to be the genuine ksh93 and not a clone.

The common ground between ksh and Bourne functionality was used to define the POSIX standard for /bin/sh, so ksh is a significant shell scripting language. In traditional Unix systems, it is quite acceptable for the root user’s shell to be set to /bin/ksh. It is the default shell on IBM’s AIX Unix. /etc/init.d scripts will still be run under the Bourne shell, but the interactive root shell can be ksh (often with the -o vi option to provide vi-like history recall).

Microsoft’s Services For Unix (SFU — now discontinued) provided an almost-compatible ksh shell for the Windows environment, although it was based on mksh, which at the time was not quite compatible with the original ksh. At http://lists.blu.org/pipermail/discuss/1998-August/002393.html ...