RegexCheatsheet

Regular expressions - quick reference (Python re syntax; most engines are similar).

Characters
  .        any character except newline (re.S makes it match newline too)
  \d \D    digit / non-digit
  \w \W    word character [A-Za-z0-9_] / non-word
  \s \S    whitespace / non-whitespace
  [abc]    one of a, b, c          [^abc]  anything except a, b, c
  [a-z0-9] ranges

Anchors
  ^  $     start / end of string (or of each line with re.M)
  \b       word boundary

Quantifiers
  *  +  ?        0+, 1+, 0 or 1 (greedy)
  {3}  {2,5}     exactly 3, between 2 and 5
  *?  +?  ??     lazy versions: match as little as possible

Groups
  (abc)          capture group
  (?:abc)        group without capturing
  (?P<year>\d{4}) named group -> m.group("year")
  a|b            alternation
  (?=x) (?!x)    lookahead / negative lookahead
  (?<=x) (?<!x)  lookbehind / negative lookbehind

Examples
  ^\d{4}-\d{2}-\d{2}$          ISO date such as 2024-03-15
  ^[\w.+-]+@[\w-]+(\.[\w-]+)+$  rough email check
  ^\s+|\s+$                    leading or trailing whitespace
  (\w+)\s+\1                  doubled word ("the the")
  ^#[0-9a-fA-F]{6}$            hex colour

Python
  import re
  re.search(r"\d+", s)              first match anywhere (or None)
  re.fullmatch(r"\d+", s)           whole string must match
  re.findall(r"\d+", s)             list of all matches
  re.sub(r"\s+", " ", s)            collapse whitespace
  re.split(r"[,;]\s*", s)           split on comma or semicolon
  pat = re.compile(r"...", re.I)    compile once, reuse; re.I = ignore case

Always use raw strings (r"...") so backslashes reach the regex engine unchanged.

Or: /edit?page=RegexCheatsheet&text=your+text&name=YourName

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