Shell and its types

Computer understand the language of 0's and 1's called binary language.

In early days of computing, instruction are provided using binary language, which is difficult for all of us, to read and write. So in OS there is special program called Shell. Shell accepts your instruction or commands in English (mostly) and if its a valid command, it is passed to kernel.

Shell is a user program or it's a environment provided for user interaction. 

Shell is an command language interpreter that executes commands read from the standard input device (keyboard) or from a file.

Shell is not part of system kernel, but uses the system kernel to execute programs, create files etc.

Several shell available with Linux including:

To find all available shells in your system type following command:

$ cat /etc/shells

Note that each shell does the same job, but each understand a different command syntax and provides

different built-in functions.

Following are the different types of Unix shells:

B shell - /bin/sh – This is the default Unix shell for many Unix operating systems .
Bourne shell was written by S. R. Bourne and its more emphasis is to use it as a scripting language rather than an interactive shell .

C-shell /bin/csh was designed to provide the interactive features lacking in b shell such as job control and aliasing .

K shell /bin/ksh – was created by David Korn and has features of both B shell and C shell along with some additional features .

Bash – the Bourne again shell was developed by GNU project .It is based on B shell language and has features of C and K shells.

tcsh is the default shell of FreeBSD and its descendants. Essentially it is C shell with programmable command line completion, command-line editing, and a few other features.

Zsh is a shell designed for interactive use and it has many of the useful features of bash, ksh, and tcsh along with many new features.