If it doesn't work on your box like on my box*es* (tested on Ubuntu and Arch), then probably your PHP setup is fuzzy or broken. If you run this command:
php -i | grep 'API'
You should see:
Server API =>CommandLineInterface
If you don't, this means that maybe another command will provides the CLI SAPI. Try php-cli, maybe it's a package or a command available in your OS.
If you do see that your php command uses the CLI (Command Line Interface) SAPI (Server API), then run php -h | grep code to find out which crazy switch - as this hasn't changed for year- allows to run code in your version/setup.
Another couple of examples, just to make sure it works on my boxes:
Also, note that it is possible that an extension is loaded in the CLI and not in the CGI or Apache SAPI. It is likely that several PHP SAPIs use different php.ini files, e.g. /etc/php/cli/php.ini vs /etc/php/cgi/php.ini vs /etc/php/apache/php.ini on a Gentoo box. Find out which ini file is used with php -i | grep ini.