In UNIX systems, the command interpreter is just an ordinary program,
reading lines from the standard input – and writes to standard output
and standard error.
Such command are called as filter in UNIX.
There are various command interpreters – shells – in UNIX systems:
- sh (Bourne shell)
- csh (C shell)
- ash (Almquist shell)
- ksh (Korn shell)
- zsh (Z shell)
- bash (Bourne-again shell)
* all files (except when starting with .),
Structure of commands
Sequence and backgrounding
Shell variables and subshells
Alternatively one can use the . command.