Strange-looking incantations that can be extremely useful at describing patterns in text. Used all over the place, primarily in Unix tools like grep and vim, and in programming languages like Perl and PHP.

There are two “flavors” of regular expressions, those which conform to the POSIX standard, and those compatible with perl. (the latter are known as Perl-compatible regular expressions; the library many tools link to is known as libpcre).

Also seen shorthand as regexp, or simply re.

Resources

• RegexPal is an interactive JavaScript tester for Regular Expressions
• (Useful) Stupid Regex Tricks from SlashDot.