A command shell is a command line interface computer program to an operating system.

Some Variants

1. Bash : Comes as default shell on ubuntu

2. KornShell(ksh) :

To install ksh in Ubuntu

   $ sudo apt-get install ksh

To start working with ksh

    $ ksh
    $ ps $$
      PID TTY      STAT   TIME COMMAND
      4187 pts/2    S      0:00 ksh

Enter the commands at the ksh prompt

3. csh :

To install csh in Ubuntu

    $ sudo apt-get install csh

To work with csh, go to the command line and enter csh

    $ csh
    %

At the command prompt:

$ echo "Hello World"

Output:

Hello World

To create a script, create a text document with the following content:

#!/bin/sh
echo "Hello World"

Save the script with the name hello.sh (or any filename) and make the script executable by giving the following permission:

$ chmod 755 hello.sh

Or:

$ chmod +x hello.sh

Run the script:

$ ./hello.sh

Output:

Hello World

To run a local shell script without executable permission:

1.bash

$ bash hello.sh
Hello World

2.ksh

$ ksh hello.sh
Hello World

3.sh

$ sh hello.sh
Hello World