Unix Shell
A shell is  command interpreter between user and Unix kernel as well as provides a strong scripting language in UNIX
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 .
Some of the features are :
Provided support for environment variables using parameters and exportable variables.
Redirection of program output and error .
Command substitution using back quotes: `command`.
embed a file/commands using input redirector <<
“for ~ do ~ done” loops
“case ~ in ~ esac” for selecting and responding to a data value .
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.

Unix Shell configuration files :


b shell
—————————————————–
shell prompt : $
executable file : /bin/sh
Read on interactive/non interactive login to bash
/etc/profile
~/.profile

bash shell
—————————————————–
shell prompt : $
executable file : /bin/bash
Read on interactive/non interactive login to bash
/etc/profile
~/.profile
~/.bash_profile
~/.bash_login
Always read on invoking bash
~/.bashrc
/etc/profile login login login
~/.profile login login

csh shell
——————————————————
shell prompt : %
executable file : /bin/csh
Read on csh shell invocation .
/etc/csh.cshrc
~/.cshrc
Read on interactive/non interactive login to tcsh shell
/etc/.login
~/.login
~/.logout
/etc/csh.login

ksh
—————————————————–
shell prompt : $
executable file : /bin/ksh
Read on interactive/non interactive login to bash
/etc/profile
~/.profile

tcsh shell
——————————————————
shell prompt : &
executable file : /bin/tcsh
Read on tcsh shell invocation .
~/.tcshrc
/etc/csh.cshrc
~/.cshrc
Read on interactive/non interactive login to tcsh shell
/etc/.login
~/.login
~/.logout
/etc/csh.login

zsh
—————————————————–
shell prompt : $
executable file : zsh
Configuration files :
Always read on invoking zsh
~/.zshenv always
/etc/zshenv always
only read on interactive login to zsh.
~/.zshrc
/etc/zshrc
Read on interactive/non interactive login to zsh
/etc/zprofile login
/etc/zlogin login
/etc/zlogout login
/.zprofile login
~/.zlogin login
~/.zlogout login