Ubuntu · Creating [Shell] Scripts

Note: This was tested on 12.04, but should work for later versions as well.

Note: You’ll see that I’m using Sublime Text as my text editor on Ubuntu desktop. You may use gedit or anything else really instead. For example, nano is a simple alternative for the Terminal. If you want to install Sublime Text, you can do a quick search for it here.

What is a bash script?

A bash script is, well… a series of Terminal commands typed together in a file, one below the other. The commands are always executed top to bottom, line by line. We often say “bash” and “shell” interchangeably, even though “bash” is a different variant of shell. For the purpose of this post, it’s the same thing.

To create a new script, you need to start writing to a file. The easiest for beginners is to use a desktop editor, like Sublime Text.

In the Terminal, type:

sublime-text myscript.sh

If you have a different version of Sublime Text, your command line tool might be called subl instead of sublime-text, so just replace it if needed.

It’s common for these scripts to have names that end with .sh, but you can name it whatever you want. When you’ve opened the empty document, add this as the first line (it basically tells the system which shell to run):

#!/bin/bash

This line tells the location of your Shell executable. It will most likely be in the default location (/bin/bash), but you can double-check by typing:

which bash

Adding commands

Ok, your file now has the executable which to use for running. Below that first line, you can add any command you want (just remember to put them each on a new line). Let’s say we want to write “Hello World” on the screen. The complete file would look like this:

#!/bin/bash 
echo Hello\ World

You can see that the space in “Hello World” is preceded with a \ character, which allows spaces to be used (note that it doesn’t work for all commands). Another way to print spaces is to put the whole output under double quotes (").

Ok, back to the main thing. Now save that file and (optionally) exit the editor. When you have done that, you have a script file waiting for you to execute it. But the script is not executable yet. The system doesn’t know that this file contains runnable commands by default.

You can enable execution for this file by right-clicking on it from the file browser, then going to Properties, and then modifying the ownership information. Set allow execution to enabled. Another (faster) way to do it is from the Terminal, like so:

chmod +x myscript.sh

There we go, your script is executable now! You can run it by using the sh command, or just by using it’s fully qualified name from the current directory:

./myscript.sh