Review of the three primary UNIX Shells

The Bourne shell was written before the other two primary shells. It has the smallest number of features of any of the shells, but is commonly used to write shell scripts. Bourne shell scripts can be run from either the Bourne or Korn shells because Korn is backwards compatible with Bourne.

The Korn shell was written last of the three primary shells. It is the Bourne shell plus some additional programming features.
The Korn shell was developed at AT&T's Bell labs.

1. The C shell was written after the Bourne shell and is not compatible with the other two shells.
2. The C shell was written at UC BerkeleyThe C shell (csh or the improved version, tcsh, on most machines) is a Unix shell that was created by Bill Joy while a graduate student at University of California, Berkeley in the late 1970s.
3. It has been distributed widely, beginning with the 2BSD release of the BSD Unix system that Joy began distributing in 1978.
4. The C shell is a command processor typically run in a text window, allowing the user to type commands.
5. Like all Unix shells, C shell supports filename wildcarding, piping, command substitution, variables and control structures for condition-testing and iteration.

What differentiated the C shell from others, especially in the 1980s, were its interactive features and overall style. Its new features made it easier and faster to use. The overall style of the language looked more like C and was seen as more readable. On many systems, such as Mac OS X and Red Hat Linux, csh is actually tcsh, an improved version of csh.

Other popular shells include the bash shell (the “Bourne again” shell), which is an enhanced Bourne shell distributed with Linux and some other UNIX systems. It is available for free on the Internet. Tcsh is another popular shell. It is a C shell with added features.