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I just want to say, please do not make broad sweeping claims about the history of regular expressions if you do not know it. They were not designed to work with the Unix file system, they were implemented this way, yes. However, a simple search on Google for "history of regular expressions" will bring you many pages. the first is the Wikipedia article, which explains it nicely.

http://en.wikipedia.org/wiki/Regular_expression#History

Sorry, I don't mean to go off on tangents on related to the spirit of the article, but I hate the idea that misinformation like this can spread and become fact for many people.

Also, please do not use the prescribed regex for email addresses. It is too strict and does not match all valid addresses.

None of these will match this check, but should:

email.address@sub.server.com - valid
email#address@sub.sub.server.com - valid
email!address@server.com - valid