types of shells in unix

1. sh: 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. It was developed by Stephen Bourne, of AT&T Bell Laboratories, and was released in 1977 in the Version 7 Unix release distributed to colleges and universities. It remains a popular default shell for Unix accounts. The binary program of the Bourne shell or a compatible program is located at /bin/sh on most Unix systems, and is still the default shell for the root superuser on many current Unix implementations.

   

2. ash: The Almquist shell (also known as A Shell or ash) 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.

   

3. dash: Debian Almquist shell (dash) is a POSIX-compliant Unix shell, much smaller than bash. It requires less disk space but is also less feature rich. dash is a direct descendant of the NetBSD version of the Almquist Shell (ash). It was ported to Linux by Herbert Xu in early 1997. It was renamed to dash in 2002.dash executes scripts faster than bash and depends on fewer libraries. It is believed to be more reliable in case of upgrade problems or disk failures.

   

4. bash: Bash is a Unix shell written for the GNU Project. The name of the actual executable is bash. Its name is an acronym for Bourne-again shell, a pun on the name of the Bourne shell (sh) (i.e. “Bourne again” or “born again”), an early and important Unix shell written by Stephen Bourne and distributed with Version 7 Unix circa 1978. Bash was created in 1987 by Brian Fox. In 1990 Chet Ramey became the primary maintainer. Bash is the default shell on most Linux systems as well as on Mac OS X and it can be run on most Unix-like operating systems.

   

5. fish: fish is a Unix shell. Its name is an acronym for friendly interactive shell. fish focuses on interactive use, discoverability, and user friendliness. The design goal of fish is to give the user a rich set of powerful features in a way that is easy to discover, remember, and use.

   

6. ksh: 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. The main advantage of ksh over the traditional Unix shell is in its use as a programming language. Since its conception, several features were gradually added, while maintaining strong backwards compatibility with the Bourne shell.

   

7. csh: The C shell (csh) is a Unix shell developed by Bill Joy for the BSD Unix system. It was originally derived from the 6th Edition Unix /bin/sh (which was the Thompson shell), the predecessor of the Bourne shell. Its syntax is modeled after the C programming language. The C shell added many feature improvements over the Bourne shell, such as aliases and command history. Today, the original C shell is not in wide use on Unix; it has been superseded by other shells such as the Tenex C shell (tcsh) based on the original C shell code, but adding filename completion and command line editing, comparable with the Korn shell (ksh), and the GNU Bourne-Again shell (bash).

   

8. tcsh: tcsh (pronounced “TC-Shell” or “T-shell”) is a Unix shell based on and compatible with the C shell (csh). It is essentially the C shell with (programmable) filename completion, command-line editing, and a few other features.

   

9. es: The es shell is a command line interpreter that uses a scripting language similar to the rc shell. It is intended to provide a fully functional programming language as a Unix shell. The bulk of es’ development occurred in the early 1990s. Unlike other modern shells, es does not have job control. Patches to provide job control have been offered, but the currently available ones have memory leak problems.

   

10. rc: rc is the command line interpreter for Version 10 Unix, Plan 9, and Inferno operating systems. It resembles the Bourne shell, but its syntax is somewhat simpler. It was created by Tom Duff, who is better known for an unusual C programming language construct called Duff’s device.

    

11. scsh: Scsh is a POSIX API layered on top of the Scheme programming language (currently only a Scheme 48 implementation exists, but others are planned) in a manner to make the most of scheme’s capability for scripting. It is limited to 32-bit platforms.

12. sash: Stand-alone shell (sash) is a Unix shell designed for use in recovering from certain types of system failures. The built in commands of sash have all libraries linked statically, so unlike most shells, the standard UNIX commands do not rely on external libraries. For example the copy command (cp) requires linux-gate.so, libc.so, and ld-linux.so when built from GNU coreutils on Linux. If any of these libraries get corrupted, the coreutils cp command would not work, however in sash, the built-in command, cp, would be unaffected.

    

13. zsh: The Z shell (zsh) is a Unix shell that can be used as an interactive login shell and as a powerful command interpreter for shell scripting. Zsh can be thought of as an extended bourne shell with a large number of improvements, including some of the most useful features of bash, ksh, and tcsh.