}}The '''UNIX Shell''' is a component of terminal-based [[UNIX]]-derived systems which offers both a command-line interface for running system commands, as well as programming interface for intelligently automating tasks which use system commands.
There are many UNIX Shells and most of them can be categorized into two families. For purposes of the Rosetta Code, all examples are in Bourne-compatible syntax. The other family of shells, with a markedly different syntax, are ''csh'' ([[:Category:C Shell|C Shell]]) and its ''tcsh'' (Tenex C Shell) "clone." Common Bourne compatible shells include the original [[Bourne Shell]] (''/bin/sh'' on most versions of UNIX), the GNU [[Bourne Again SHell]] (''bash'' --- which is linked to ''/bin/sh'' on many distributions of [[Linux]], making it their default shell), the [[Korn Shell]] (''ksh''), the [[Public Domain Korn SHell]] (''pdksh''), the [[Almquist SHell]] (''ash'') and the [[Debian Almquist SHell]] (''dash'') and the [[Z SHell]] (''zsh'').
While UNIX Shells vary in the programming languages they support, such languages carry a minimum set of features. Each language allows the programmer to [[Execute a System Command|execute system commands]] as though he were typing the commands himself, and each language allows for a header line which specifies which shell implementation is used to interpret the script.
This one tells the operating system to use the [[Bourne Shell]]:
#!/bin/sh
This line tells the operating system to use the [[Bourne Again SHell]]:
#!/bin/bash
And this one tells the operating system to use the [[Korn Shell]]:
#!/bin/ksh
Each header line consists of a hash, a bang, and the path to the [[interpreter]] binary.
