On vary rare occasion I find it useful to run php in the command line.
There are a couple of easy ways to do this, but the first thing you might want to do is check your php version.
This is easily done with the following command:
php -v
Then if you want to quickly execute some php directly in the terminal you can use the -r switch:
php -r 'echo "Boo!";'
But if you want to run some more complex php you'll probably want to code it up in a file and then run that from the command line like so:
php -f my-great-php-file.php