Common shells in Un*x:
ash free
sh Bourne proprietary
bash Bourne-Again GNU GPL
csh C proprietary (see tcsh)
ksh KornShell proprietary. new ``open'' license.
pdksh Public Domain Korn Shell free
tcsh enhanced C free
zsh Z free

KornShell for Linux and other systems, and other products can be obtained directly from GTL. Note that it comes with a restrictive license -- it is not Free. There are new pseudo- ``open source'' licensing terms available, which we will learn when David Korn comes to the Jan. 2001 NYLUG meeting.

1. ksh93 binaries ATT
2. pdksh source code
3. AT&T ksh93
4. The New KornShell -- ksh93 Linux Journal
5. KornShell Documentation
6. RayCosoft unixscripts.com
7. Csh Programming Considered Harmful
   
   Free software alternatives include:
   the GNU Bourne-Again Shell Bash,
   the Public Domain KornShell and the
   Z shell .
   From the zsh manual:

   DESCRIPTION Zsh is a UNIX command interpreter (shell) usable as an interactive login shell and as a shell script command pro­ cessor. Of the standard shells, zsh most closely resem­ bles ksh but includes many enhancements. Zsh has comand line editing, builtin spelling correction, programmable command completion, shell functions (with autoloading), a history mechanism, and a host of other features.

   COMPATIBILITY Zsh tries to emulate sh or ksh when it is invoked as sh or ksh respectively.

   For zsh, see the chapter in Mark G. Sobell's Practical Guide to Linux from Addison-Wesley Longman.