Regex Cheat Sheet

Regular expressions (regex) are compact patterns for matching text. They power search-and-replace, validation and data extraction. The syntax looks cryptic at first, but a handful of building blocks covers most real-world needs. Test any pattern here live in the regex tester.

Character classes

• \d — any digit (0–9). \D is any non-digit.
• \w — a word character (letters, digits, underscore). \W is the opposite.
• \s — any whitespace (space, tab, newline). \S is non-whitespace.
• . — any single character except a line break.
• [abc] — any one of a, b or c. [a-z] — any lowercase letter. [^abc] — anything except a, b or c.

Quantifiers

• * — zero or more of the preceding item.
• + — one or more.
• ? — zero or one (makes it optional).
• {3} — exactly 3. {2,5} — between 2 and 5. {2,} — 2 or more.

Anchors and boundaries

• ^ — start of the string (or line, in multiline mode).
• $ — end of the string or line.
• \b — a word boundary, e.g. \bcat\b matches "cat" but not "category".

Groups and alternation

• (...) — a capturing group; also lets a quantifier apply to several characters.
• (?:...) — a non-capturing group.
• a|b — matches a or b ("or").

Ready-to-use patterns

• Digits only: ^\d+$
• Simple email: \w+@\w+\.\w+
• Whole word: \bword\b
• Strip extra spaces: find \s{2,}, replace with a single space.
• Trailing whitespace: \s+$

Flags

Flags change how a pattern runs: g finds all matches (not just the first), i ignores case, m makes ^ and $ match per line, and s lets . match line breaks.

Using regex to clean text

Capture groups make replacements powerful: match (\w+), (\w+) and replace with $2 $1 to swap "Last, First" into "First Last". Try patterns against your own text with the find and replace tool, which supports regex and capture groups.