LINUX shells

DEFINITION

• Shell is an command language interpreter that executes commands read from the standard input device ( keyboard ) or from a file.
• Shell is a user program or it's environment provided for user interaction.
• The shell accepts a user’s entries, interprets them, converts them to system calls, and delivers system messages back to the user.

VARIOUS LINUX SHELL

1. Bash shell (sh command)
2. C shell (csh command)
3. korn shell (ksh command)
4. tcsh shell
5. ash shell

Bash shell ( sh )

• Default shell for most Linux distro.
• Acronym for Bourne aagain Shell.
• Includes features originally developed for sh and ksh shells in early UNIX systems , as well as some csh features.

C Shell ( csh )

• csh shell was created by Bill Joy and used with most Berkeley UNIX systems (such as those produced by Sun Microsystems) as the default shell.
• Its syntax is modeled after the C programming language.
• While you can run both csh and tcsh on most Linux systems, both commands actually point to the same executable file. 

Korn shell ( ksh )

• created by David Korn at AT&T Bell Labs and is the successor to the sh shell.
• Offers rich scripting capabilities.
• became the default and most commonly used shell with UNIX System V systems.

tcsh shell

• open source version of the C shell (csh).
• Enhanced C shell with file name completion and command line editing.

ash shell

• lightweight version of the Berkeley UNIX sh shell.
• It doesn’t include many of the sh shell’s basic features, and is missing such features as command histories. Kenneth Almquist created the ash shell.
• good shell for embedded systems that have fewer system resources available.