tcsh

tcsh is an enhanced Unix shell derived from the Berkeley C shell (csh). It provides a C shell–compatible scripting language along with improved interactive features, and is widely available on many Unix-like systems, especially those of BSD heritage.

Key features of tcsh include interactive command line editing, filename completion, and extended history capabilities, along with aliases and straightforward environment management. It maintains compatibility with the C shell syntax, making scripts written for csh generally usable in tcsh, though there are occasional differences that can affect portability.

In terms of language and syntax, tcsh supports the C shell control structures such as foreach, while, if, switch, and end, as well as commands for variables, environment settings, and path handling via set and setenv. It also includes conveniences common to tcsh users, such as alias definitions and simple substitutions, which aid in interactive use and routine scripting.

History and licensing: tcsh originated as an extended version of the C shell and has been maintained by contributors across Unix-like systems. It is not POSIX sh–compatible and is typically used for interactive work or scripts written for csh/tcsh rather than for portable system scripts.

Availability and usage: tcsh is distributed under a BSD-style license and is available as a package on many systems. It may be installed by default on some BSD-derived systems and can usually be selected as an alternative to other shells. To run tcsh, you can type tcsh at the command line; on many systems, it can be set as the default login shell with an appropriate user management command.