There are countless such scripts available from sites such as http://www.freshmeat.net (including this one, this one and this one).

On this site, I simply typed Link Checker into the search box and sure enough, an excellent example from tachyon was found here - In addition to checking href links, this script also checks img links and mailto links (for RFC822 compliance).

 

perl -e 's&&rob@cowsnet.com.au&&&split/[@.]/&&s&.com.&_&&&print'