I Used the code given in the example solution but for some reason when I type the command one of the three commands I got the following error

Hi @s.albuqami,

The problem is that you are typing the argument after the script has finished, then when you type `forward_backward`, bash complains that the command does not exist.

The way you have to call your script is:

``````./ex3_4_script.sh forward_backward
``````

rather than

``````./ex3_4_script.sh

# script finished here

forward_backward
``````