Regular Expressions

Regular Expressions is a name given to a way of matching text strings with a specially-coded pattern. You can really think of regular expressions as another language. Various programming and scripting languages (e.g. Perl, PHP, ColdFusion, JavaScript*, C, C#, Visual Basic, Java) can recognize this language/code and help you find what you're looking for.

Sample Text String: Congratulations, Phil Smith, your social security number is 123-45-6789. Be sure to keep it safe.

If you were to want to search through that text string and find the social security number, a RegEx can make your job much easier. The following RegEx will find the social in the above text string.

[0-9]{3}-[0-9]{2}-[0-9]{4}

RegEx Insight

The following guidelines will help you as you learn to work with RE's...

Not all languages support the same style regular expressions as the others. Usually the differences are only slight, and only among the more complex features. This means that a RegEx used in a Perl program to validate email addresses may not work exactly the same way if you were to copy it over into one of your Java programs.
Some characters of the RE language represent characters in your test string (e.g. the period), while some represent how many times the preceding character should occur (e.g. the question mark, plus sign, asterisk, and a number in braces)

Sample RegEx for email addresses

^(([[:alnum:]!##-'*+-/=?^`{-~]+(.[[:alnum:]!##-'*+-/=?^`{-~]+)*)|(.+))@((([[:alnum:]]+[[:alnum:]-]*[[:alnum:]]+.)+[[:alpha:]]{2,7}))$