Regex Memo

Regex cheat sheet/reference.

Runs locally

Character Classes

Any character

Matches any single character except newline.

Example: a.b

Matches "axb", "a2b", "a*b"

Character Classes

Digit

Matches any digit character (equivalent to [0-9]).

Example: \d+

Matches "123", "0", "999"

Character Classes

Non-digit

Matches any non-digit character (equivalent to [^0-9]).

Example: \D+

Matches "abc", "hello", "-*"

Character Classes

Word character

Matches alphanumeric characters and underscore (equivalent to [a-zA-Z0-9_]).

Example: \w+

Matches "user_name", "helper1"

Character Classes

Non-word character

Matches any character that is not a word character.

Example: \W+

Matches "!", " @ ", " - "

Character Classes

Whitespace

Matches whitespace characters including space, tab, newline.

Example: a\sb

Matches "a b", "a\tb"

Character Classes

Non-whitespace

Matches any character that is not a whitespace.

Example: \S+

Matches "hello", "123", "!"

Character Classes

[abc]

Character set

Matches any single character listed inside the brackets.

Example: [aeiou]

Matches "a", "e", "i" (vowels)

Character Classes

[^abc]

Negated character set

Matches any single character not listed inside the brackets.

Example: [^0-9]

Matches "a", "x", "-", " "

Character Classes

[a-z]

Range

Matches any character in the specified range.

Example: [a-z]

Matches "a", "k", "z"

Anchors

Beginning of line

Matches the beginning of the string or line.

Example: ^hello

Matches "hello world", but not "say hello"

Anchors

End of line

Matches the end of the string or line.

Example: world$

Matches "hello world", but not "world map"

Anchors

Word boundary

Matches a word boundary position (between a word character and a non-word character).

Example: \bcat\b

Matches "cat", but not "concat" or "cats"

Anchors

Non-word boundary

Matches any position that is not a word boundary.

Example: \Bcat

Matches "concat", "copycat", but not "cat"

Quantifiers

Zero or more

Matches the preceding element zero or more times.

Example: ab*

Matches "a", "ab", "abbb"

Quantifiers

One or more

Matches the preceding element one or more times.

Example: ab+

Matches "ab", "abbb", but not "a"

Quantifiers

Zero or one

Matches the preceding element zero or one time.

Example: ab?

Matches "a", "ab"

Quantifiers

{n}

Exactly n times

Matches the preceding element exactly n times.

Example: a{3}

Matches "aaa"

Quantifiers

{n,}

At least n times

Matches the preceding element at least n times.

Example: a{2,}

Matches "aa", "aaa", "aaaa"

Quantifiers

{n,m}

Between n and m times

Matches the preceding element between n and m times.

Example: a{2,4}

Matches "aa", "aaa", "aaaa"

Groups & References

(abc)

Capturing group

Groups multiple tokens together and creates a capture group for extracting substrings.

Example: (abc)+

Matches "abc", "abcabc"

Groups & References

(?:abc)

Non-capturing group

Groups multiple tokens together without creating a capture group.

Example: (?:abc)+

Matches "abc", "abcabc"

Groups & References

a|b

Alternation

Matches either the element before or the element after the pipe.

Example: cat|dog

Matches "cat", "dog"

Lookarounds

(?=abc)

Positive lookahead

Asserts that the preceding element is followed by the lookahead group.

Example: a(?=b)

Matches "a" in "ab", but not "a" in "ac"

Lookarounds

(?!abc)

Negative lookahead

Asserts that the preceding element is not followed by the lookahead group.

Example: a(?!b)

Matches "a" in "ac", but not "a" in "ab"

Lookarounds

(?<=abc)

Positive lookbehind

Asserts that the following element is preceded by the lookbehind group.

Example: (?<=a)b

Matches "b" in "ab", but not "b" in "cb"

Lookarounds

(?<!abc)

Negative lookbehind

Asserts that the following element is not preceded by the lookbehind group.

Example: (?<!a)b

Matches "b" in "cb", but not "b" in "ab"

Flags

Global search

Retain the index of last match, allowing iterative matches across the input.

Example: /a/g

Finds all "a" occurrences in "banana"

Flags

Case-insensitive search

Ignore case differences when matching letters.

Example: /hello/i

Matches "Hello", "HELLO", "heLLo"

Flags

Multiline search

Changes behavior of ^ and $ to match start/end of lines, not just strings.

Example: /^a/m

Matches "a" at start of newlines inside a block

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