What is a bash script

A bash script is a simple file that contains ASCII text intended to be interpreted by the program bash, allowing you to do a logical sequence of actions by calling a simple line command instead of typing them one at a time in the shell.

The first line of a script should always tell the shell which program should interpret it:

#!/bin/bash
echo "Hello World, I am a 42 student!"

In this case, the script should be interpreted by /bin/bash and say Hello when it is invoked. To invoke the script, you can type sh scriptname or make it executable with a chmod:

[shell prompt]$ chmod 755 scriptname
[shell prompt]$ ./scriptname

Bash has a lot of builtin functions and enables you to write some real applications with variables, conditions, functions... You first need to learn a bit of its syntax ;-)