Regex Cheatsheet

Character Classes

Pattern	Description
.	Any character except newline
\d	Digit [0-9]
\D	Non-digit [^0-9]
\w	Word character [a-zA-Z0-9_]
\W	Non-word character
\s	Whitespace [ \t\n\r\f\v]
\S	Non-whitespace
[abc]	Any of a, b, or c
[^abc]	Not a, b, or c
[a-z]	Range: a to z
[a-zA-Z]	Any letter
[0-9]	Any digit

Anchors

Pattern	Description
^	Start of string (or line with m flag)
$	End of string (or line with m flag)
\b	Word boundary
\B	Non-word boundary
\A	Start of string (absolute)
\Z	End of string (absolute)

Quantifiers

Pattern	Description
*	0 or more
+	1 or more
?	0 or 1
{3}	Exactly 3
{3,}	3 or more
{3,5}	Between 3 and 5
*?	0 or more (lazy)
+?	1 or more (lazy)
??	0 or 1 (lazy)

Groups & References

Pattern	Description
(abc)	Capturing group
(?:abc)	Non-capturing group
(?<name>abc)	Named capturing group
\1	Backreference to group 1
\k<name>	Backreference to named group
(a|b)	Alternation: a or b

Lookaround

Pattern	Description
(?=abc)	Positive lookahead
(?!abc)	Negative lookahead
(?<=abc)	Positive lookbehind
(?<!abc)	Negative lookbehind

Flags

Flag	Description
g	Global: match all occurrences
i	Case-insensitive
m	Multiline: ^ and $ match line boundaries
s	Dotall: . matches newline
u	Unicode support
x	Extended: allow whitespace and comments

Escape Sequences

Pattern	Description
\\	Literal backslash
\.	Literal dot
\*	Literal asterisk
\+, \?, \^, \$	Literal special characters
\[, \], \(, \)	Literal brackets/parens
\{, \}, |	Literal braces/pipe

Common Patterns

# Email (simplified)
[\w.-]+@[\w.-]+\.\w{2,}

# URL
https?://[\w\-.]+(:\d+)?(/\S*)?

# IPv4 address
\b\d{1,3}(\.\d{1,3}){3}\b

# Date (YYYY-MM-DD)
\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])

# Phone (US)
\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}

# Hex color
#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})

# HTML tag
<\/?[\w\s="'-]*\/?>

# Whitespace trimming
^\s+|\s+$

# Duplicate words
\b(\w+)\s+\1\b

JavaScript Usage

const re = /pattern/flags;
re.test("string");           // true/false
"string".match(re);          // match array or null
"string".replace(re, "new"); // replaced string
"string".split(re);          // split into array
[..."string".matchAll(re)];  // all matches (with g flag)

Python Usage

import re
re.search(r"pattern", string)    # First match or None
re.match(r"pattern", string)     # Match at start only
re.findall(r"pattern", string)   # List of all matches
re.sub(r"old", "new", string)    # Replace all
re.split(r"pattern", string)     # Split by pattern
re.compile(r"pattern")           # Precompile for reuse