What is Linux Shell?

• In Operating System, 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.
• 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.
• In MS-DOS, Shell name is COMMAND.COM which is also used for same purpose, but it's not as powerful as our Linux Shells are!
• To find your current shell type following command

  $ echo $SHELL
  

• To use shell (You start to use your shell as soon as you log into your system) you have to simply type commands.