If you use BBEdit to work with text files, you're certainly aware of its powerful regular expression feature for searching and replacing text. Based on the PCRE (Perl Compatible Regular Expressions) engine, the BBEdit regex language can find and replace pretty much anything.
GitHub user ccstone has published a BBEdit Regular Expression Cheat Sheet, which shows all the standard regex meta-characters, those used for non-visible characters (such as tabs and returns), and classes (such as digits, lower-case letters or alphanumeric characters).
If you use BBEdit to find and replace text, and especially if you're not familiar with using regular expressions, you should bookmark this page.
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http://hints.macworld.com/article.php?story=20130419012508674