Csh

CSH commonly refers to the C shell, a Unix shell and command language named for its C-like syntax. In some references the acronym appears as CSH, though the program is usually invoked as csh. The C shell is primarily noted for its interactive use and scripting capability.

The C shell was developed by Bill Joy at the University of California, Berkeley in the late 1970s for BSD Unix. It introduced features aimed at interactive work, including command history, a built-in editor or line-editing facilities in later variants, and job control. Its design influenced later shells and contributed to the development of enhanced versions such as tcsh.

Features and syntax of the C shell emphasize a C-inspired approach to scripting. Its control structures include if (condition) then ... endif, foreach var (list) ... end, while (condition) ... end, and switch ... endsw. It uses startup files like .cshrc to configure the user environment and define aliases. The shell also supports features such as aliasing, directory stacks, and basic job control for managing foreground and background processes.

Usage and modern status: While once common on BSD and other Unix systems, csh has largely declined for scripting in favor of Bourne-like shells such as sh, ksh, and Bash, which offer more consistent syntax and scripting capabilities. C shell remains available on many systems and is still used interactively in some environments or maintained for legacy scripts. The tcsh variant provides improved interactive features, including enhanced command-line editing and filename completion.