PHP正则表达式替换配置文件中的值

I need to use php to find and replace the database in a config file:

$cfg['database'] = 'my_database_name';

Basically, I'm trying to figure out a regular expression that would find everything between

 $cfg['database'] = 

and

;

then replace it with the actual database name. I think I would need to use preg_replace and then use the matches array, but I'm having a hard time trying to make it work.

Can someone give me an idea of how to go about this, or point me to a good resource that would address this specific type of replacement situation?