Unix shell 家谱

Thompson shell
The Thompson shell was the first Unix shell, introduced in the first version of Unix in 1971, and was written by Ken Thompson.

Bourne shell
The Bourne shell, or sh, was the default Unix shell of Unix Version 7, and replaced the Thompson shell, whose executable file had the same name, sh.

Korn shell
The Korn shell (ksh) is a Unix shell which was developed by David Korn (AT&T Bell Laboratories) in the early 1980s. It is backwards-compatible with the Bourne shell and includes many features of the C shell as well, such as a command history, which was inspired by the requests of Bell Labs users.

Bash(derive for Bourne shell)
Bash is a free software Unix shell written for the GNU Project. Its name is an acronym which stands for Bourne-again shell.^[1] The name is a pun on the name of the Bourne shell (sh), an early and important Unix shell written by Stephen Bourne and distributed with Version 7 Unix circa 1978,^[2] and the concept of being "born again". Bash was created in 1987 by Brian Fox. In 1990 Chet Ramey became the primary maintainer.^[3]

Almquist shell(derive for Bourne shell)
The Almquist shell (also known as A Shell, ash and sh) was originally Kenneth Almquist's clone of the SVR4-variant of the Bourne shell; it is a fast, small, POSIX-compatible Unix shell designed to replace the Bourne shell in later BSD distributions. By intention it did not feature line editing or command history mechanisms originally, because Almquist felt that such should be moved into the terminal driver. Current variants have emacs and vi modes.

Debian Almquist shell(derive for Almquist shell)
Debian Almquist shell (dash) is a Unix shell, much smaller than bash but still aiming at POSIX-compliancy. It requires less disk space but is also less feature-rich. Some missing features, such as the $LINENO variable, are required by POSIX.