The C shell (
csh) is one of the two major historical command line processors on Unix systems, the other one being the Bourne shell (
sh). A modified Bourne shell went on to be standardized by POSIX, while use of the C shell has declined.
Csh and its derivative tcsh were widely considered to have superior interactive features but inferior programming features. Newer shells such as zsh and bash have since then acquired and surpassed tcsh's interactive features such as advanced command line edition and programmable completion, while the csh family has seen little evolution since the late 1990s.