Joshua Wood Web Developer

Regular Expressions

Regular expressions are worth learning. I keep some of the trickier syntax on this page for quick reference.

Lookarounds

Lookarounds are useful when you want to match (or exclude) results based on what comes before or after the current position.

Name Expression Description
Lookahead (?=pattern) Asserts that the string following the current position is “pattern”
Negative Lookahead (?!pattern) Asserts that the string following the current position is not “pattern”
Lookbehind (?<=pattern) Asserts that the string preceding the current position is “pattern”
Negative Lookbehind (?<!pattern) Asserts that the string preceding the current position is not “pattern”

Useful Tools

Rubular: a Ruby regular expression editor