Regex Cheat Sheet: Common Patterns for Developers
This regex cheat sheet provides a quick reference for the most common regular expression patterns and syntax. Whether you are validating input, extracting data from text, or building search-and-replace operations, these patterns cover the vast majority of real-world use cases.
Anchors and Boundaries
Anchors match positions rather than characters. The caret (^) matches the start of a line, and the dollar sign ($) matches the end. Together, ^pattern$ ensures the entire string matches the pattern with nothing extra. The word boundary \b matches the position between a word character and a non-word character — useful for matching whole words without picking up substrings.
For example, \bcat\b matches "cat" in "the cat sat" but not in "category." Without word boundaries, a simple search for "cat" would match inside longer words, producing false positives in search and replace operations.
Character Classes and Quantifiers
Character classes define a set of characters to match. [a-z] matches any lowercase letter, [0-9] matches any digit, and [^a-z] matches anything that is not a lowercase letter. Shorthand classes simplify common sets: \d for digits, \w for word characters (letters, digits, underscore), \s for whitespace, and their uppercase inverses \D, \W, \S for the opposite.
Quantifiers control how many times a pattern repeats. The asterisk (*) means zero or more, the plus (+) means one or more, and the question mark (?) means zero or one. Curly braces specify exact counts: {3} means exactly three, {2,5} means two to five, and {3,} means three or more. By default, quantifiers are greedy (match as much as possible); adding ? makes them lazy (match as little as possible).
Groups and Lookaheads
Parentheses create capturing groups that extract matched substrings. The pattern (\d{3})-(\d{4}) on "555-1234" captures "555" in group 1 and "1234" in group 2. Non-capturing groups (?:pattern) group without capturing, which is useful when you need grouping for alternation but do not need the matched text.
Lookaheads assert what follows without consuming characters. A positive lookahead (?=pattern) succeeds if the pattern matches ahead; a negative lookahead (?!pattern) succeeds if it does not. For example, \d+(?= dollars) matches "100" in "100 dollars" but not in "100 euros." Lookbehinds work the same way but check what precedes the current position.
Common Practical Patterns
Email validation (simplified): ^[\w.+-]+@[\w-]+\.[a-zA-Z]{2,}$ matches most standard email addresses. URL matching: https?://[\w.-]+(?:/[\w./-]*)? covers HTTP and HTTPS URLs. IP address: \b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b matches IPv4 format (though it does not validate ranges). Phone numbers vary by locale, but \+?\d[\d\s()-]{7,}\d captures most international formats.
The best way to learn regex is to experiment with a live tester. Paste your text, write a pattern, and see matches highlighted in real time. Adjust the pattern until it matches exactly what you need and nothing more.
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