GDL must be setup so that you can always run any of the programs you've written or downloaded regardless of your current directory. The first thing you must do is to setup an GDL directory. You can put this GDL directory anywhere you want and you can call it anything you want. From now on, all code you write or download must go into your GDL folder. Note: It's ok to create folders within your GDL directory. Once you've created you're GDL directory, open a terminal and type the following into the command propmpt.

>> emacs .bashrc

If you don't have emacs installed, then this will not work. Emacs is just a text editor. Any text editor will work. You just need to open .bashrc in a text editor. Now add the following lines at the end of the .bashrc file (ignoring >> ).

>> IDL_DIR=The path to your GDL directory
>> IDL_STARTUP="path to your GDL directory/.idl_startup.pro"
>> export IDL_STARTUP

You need to download idl_startup.pro and place it in your GDL directory. Now you must open the idl_startup.pro and insert the path to your GDL directory.

Everything should be ready to go. Just open up a terminal and type in gdl.