On his blog today Sameer Borate has posted a quick tutorial on how to use a PEAR package to do search and replace on your files from inside of PHP.

Searching and replacing content in files is a common task all of us do regularly. [...] Search/replace is easier from a shell prompt or an editor, but what if you have to do the same programatically in php. File_SearchReplace is a pear package that helps you search/replace in files through a nice object oriented interface.

Installation is simple (via the "pear" command line tool) and using it is just as easy. He gives a few examples of how it can be used - everything from a simple find and replace out to a more complicated regular expression search to be replaced with a string.