Option to display control characters in gedit

Solution 1:

There is a gedit-plugins package available for Ubuntu. Install that and take a look at the Draw Spaces section in the gedit preferences. You can configure it to show spaces, tabs, line feeds etc.

You can use this command in a terminal: sudo apt-get install gedit-plugins

Solution 2:

As said in the other answer you need to install the Draw-Spaces plugin in gedit. Once there, I must say, the plugin options are confusing because the word "space" is used with two different meanings, as separation character (including tab) or as a proper space.

For most applications you need these options. These specific combinations will show leading and trailing proper spaces but not show tabs. This way you can, for example, tell if indentation was not done with tabs.