I ran into a small problem in that the Command-Line-Interface PHP binary was different to the one running on my Apache+Mysql+PHP stack so the CLI PHP didn’t know which MySQL socket to attach to:

Warning: mysqli_connect(): (HY000/2002): Can’t connect to local MySQL server through socket ‘/var/mysql/mysql.sock’

The solution is simple. I am using Mac OSX 10.5.4 Leopard and XAMPP.

1. Find out which PHP you are using from the terminal by typing ‘whereis php’. It is no doubt /usr/bin/php.
   
2. Create a php.ini in /etc. Type ‘sudo cp /etc/php.ini.default /etc/php.ini
3. Then open this new file in something… I did a ‘sudo nano /etc/php.ini’.
4. Edit the mysqli.default_socket parameter (or mysql if you aren’t using the new improved driver) to point to the MySQL socket Apache is using. Mine was at /Applications/xampp/xamppfiles/var/mysql/mysql.sock (your’s may be at /tmp/mysql.sock)
5. Be sure to save this new php.ini. Remember, /etc is protected so you won’t be able to save the file unless you have sudo’d yourself admin rights.
   
6. Commenter ferzkopp kindly reminds us that an Apache restart may be neccesary to get this activated. Thanks for the Tip!

Hope this helps!