I've noticed that Richard Heyes, who professes himself to be a php guru, deleted my comment on his "Some common regular expressions" posting which simply pointed out his expressions didn't quite do the job and suggested a few PEAR packages that should be used instead of the expressions that he proffered

His examples have the benefit of what he calls "defense in depth" - the functionality to catch a bit more than just a regular expression can alone. His examples include PEAR_Validate for email addresses, Net_CheckIP2 for IP addresses and the Validate_UK package for the sort code and telephone numbers.

A coworker of mine has been working on a ajax enabled regex tool which lets you evaluate regex expressions in several languages (including PHP PCRE and PHP POSIX) with instant results.

The tool lets you put in the string you want to match again and the pattern you want to match with. The results are automatically populated below it, making it easy to fine-tune your expression to only what you want.

When it comes to quickly dealing with large blocks of data, batch processing operations or screen scraping, regular expressions are often the most effective solution. There's just one problem, though - learning them can be as hard as learning a new language altogether. Here's how to get off to a flying start.

He points you first in the direction of the preg_* functions then towards a few examples (like with mod_rewrite) and tools to help you understand how things match, like the regex tested extension for firefox and the regular expression cheat sheet on ILoveJackDaniels.com.

Recently I experimented a bit with an Apache log file analyzer written in PHP. It's not all that difficult were it not for trying to parse the browser, or user agent, string. [...] For my purposes I don't care much for the operating system details. This is the result so far. I'm still not very satisfied but I thought maybe other people might be interested and maybe help out.

He provides the code in the format of an encapsulated PHP function that returns the product they're using, the version number of the browser and other various comments.