Shell Script - Introduction

What is a Shell Script

A shell script is a file containing a series of commands. When we execute the file the shell will run the commands specified in the file which allows us to automate a lot of tasks, simple or complex. Over the years many shells have been developed, like Bourne shell (sh), Bourne Again shell (bash), Korn shell (ksh), and C shell (csh) each with its own scripting language. The shell we are going to use is the Bourne Again shell or Bash.

Basic Script file

Create a file named hello.sh (the .sh extension is just convention and therefore optional), in this example, we are going to use Vim but you can the text editor you like.

$ vim hello.sh

Copy the following text to your new file:

#!/bin/bash

echo "Hello World"

The first line of the file is a very important one because it will tell the shell what program it should use to interpret the script. In this case, it will use bash, located at /bin/bash.

The last line will run the echo command which will print Hello World in the terminal.

Run script

To run the script we need to give ourselves permission to execute the file. To do that we have to run the following command:

$ chmod +x hello.sh

Now we can run the script:

./hello.sh
Hello World