Ubuntu: Up and Running

Shell Scripts

A shell script is a sequence of command-line commands brought together into a single file to work like a small program. Let’s make a simple Hello World script by entering the following command to call up Nano ready to create the file hello in your home folder:

nano ~/hello

Now enter the following two lines into the editor, pressing Enter after each. Then press Ctrl-X, followed by y to confirm, and then Enter to save the file:

#!/bin/sh
echo "Hello World\n"

The first line, #!/bin/sh, tells Ubuntu to use the /bin/sh shell program to execute the following commands. It could equally have requested /bin/bash or another shell, but I have chosen to use /bin/sh for this example. The second line prints the text Hello World followed by a blank line, specified by the \n at the end.

Once you have saved this file, you then need to make it executable by entering the following command:

chmod +x ~/hello

The chmod command stands for change mode, and +x tells Ubuntu to make the file executable. See the section File and Folder Permissions for more details on this command.

You are now ready to run your script by entering the following. Afterward, you should see the welcoming message followed by a blank line, and then the command-line prompt:

~/hello

As I said, any commands you can enter at the command line can be used in a shell script, and that includes the use of environment variables, or even creating new variables of your own. For example, here’s an improved version of the previous script that ...