Regular Expression Cheatsheet

Quick reference for common regex patterns

Character Classes Anchors Quantifiers Groups Lookarounds Common Patterns

A Character Classes

Character Meaning Example
. Any character (except newline) a.c matches "abc", "a1c"
\d Digit [0-9] \\d with quantifier matches 3 digits like "123"
\D Non-digit [^0-9] \D+ matches "abc"
\w Word character [a-zA-Z0-9_] \w+ matches "hello123"
\W Non-word character \W+ matches "!@#"
\s Whitespace \s+ matches " "
\S Non-whitespace \S+ matches "abc"
[abc] Character set (a or b or c) [abc] matches "a", "b", "c"
[^abc] Negated set (not abc) [^abc] matches "d", "e", "f"
[a-z] Range (lowercase letters) [a-z]+ matches "hello"

B Anchors (Position Matching)

Character Meaning Example
^ Start of string ^hello matches "hello" at start
$ End of string world$ matches "world" at end
\b Word boundary \btest\b matches word "test"
\B Non-word boundary \Btest\B matches "test" in "atestb"

C Quantifiers

Quantifier Meaning Example
* 0 or more times \d* matches "", "1", "123"
+ 1 or more times \d+ matches "1", "123"
? 0 or 1 time \d? matches "", "1"
n Exactly n times Digit with brackets n means exactly n times, like \\d3 matches 3 digits
n, At least n times Digit with brackets n, means at least n times, like \\d2, matches 2 or more digits
n,m n to m times Digit with brackets n,m means n to m times, like \\d2,4 matches 2 to 4 digits

πŸ’‘ Greedy vs Lazy

By default, quantifiers are greedy (match as much as possible). Add ? to make them lazy (match as little as possible).

  • β€’ *?, +?, ??, n,m? are lazy versions
  • β€’ .* greedily matches as much as possible
  • β€’ .*? lazily matches as little as possible

D Groups and References

Syntax Meaning Example
(abc) Capturing group Parentheses capture matched content for later use
(?:abc) Non-capturing group Parentheses only for grouping, don't capture content
\1 Backreference to group 1 (\w)\1 matches "aa", "bb"
| OR operator a|b matches "a" or "b"

E Lookarounds

Syntax Meaning Example
(?=abc) Positive lookahead (followed by abc) \d(?=px) matches "1" in "1px"
(?!abc) Negative lookahead (not followed by abc) \d(?!px) matches "1" in "1ab"
(pos-lookbehind-abc) Positive lookbehind (preceded by abc) (pos-lookbehind-$)\d+ matches "100" in "$100"
(neg-lookbehind-abc) Negative lookbehind (not preceded by abc) (neg-lookbehind-$)\d+ doesn't match "$100"

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