I see you're using gphpedit, which is a *nix app I believe. If you're using Linux Mint or Ubuntu, you will need to install PHP first.
To get php to run in the Terminal, you will need to issue the following commands - in order:-
sudo apt-get update
sudo apt-get install php5-cli
Once this is complete, you can run a PHP script like so...
sudo clear && sudo php -f path/to/php/file.php
For example, if your php script was saved in your Documents folder as script.php, you would execute...
sudo clear && sudo php -f ~/Documents/script.php