Regular Expressions (Regex) Cheat Sheet

1. Basic Matching

1.1 Explicit Characters

Most characters match themselves literally.

Example	Description	Matches	Does NOT Match
/hello/	Matches the exact sequence "hello"	"hello world"	"Hello", "helo"
/123/	Matches the exact sequence "123"	"abc123xyz"	"12", "456"
/Carsten/	Matches the exact sequence of "Carsten"	"Carsten" "Hi, Carsten"	"carsten", "Karsten"

1.2 Escaping Special Characters

Some characters have special meanings in regex (see below). To match them literally, you must escape them with a backslash (\).

Special Character	Meaning in Regex	Escaped Version	Matches
.	Matches ANY single character (except newline, usually)	\.	"."
*	Quantifier (zero or more)	\*	"*"
+	Quantifier (one or more)	\+	"+"
?	Quantifier (zero or one)	\?	"?"
[	Start of a character class	\[	"["
]	End of a character class	\]	"]"
(	Start of a capturing group	\(	"("
)	End of a capturing group	\)	")"
{	Start of a quantifier with curly braces	\{	"{"
}	End of a quantifier with curly braces	\}	"}"
^	Anchor (start of string) or negation (inside [])	\^	"^"
$	Anchor (end of string)	\$	"$"
|	Alternation (OR)	\|	"|"

Example:

Example	Description	Matches	Does NOT Match
/\./	Matches a literal dot (.)	"a.b"	"ab"
/a\*b/	Matches "a", followed by zero or more "*", then "b"	"ab", "a*b"	"acb"
/\[abc\]/	Matches the literal string "[abc]"	"[abc]"	"abc"

1.3 Whitespace Characters

These are special characters that represent whitespace.

Regex	Whitespace Character	Description
\t	Tab	Matches a horizontal tab character.
\n	Newline	Matches a line break.
\r	Carriage Return	Matches a carriage return (less common on Unix).
\f	Form Feed	Matches a form feed (rarely used).
\v	Vertical Tab	Matches a vertical tab (rarely used).
	Space	Matches a single space character (explicit).

2. Quantifiers

Quantifiers specify how many times the preceding element should occur.

Quantifier	Description	Example	Matches	Does NOT Match
?	Zero or one (optional)	/colou?r/	"color", "colour"	"colouur"
*	Zero or more	/bo*a/	"ba", "boa", "booa"	"bca"
+	One or more	/lo+l/	"lol", "lool", "loool"	"ll", "lo"
{n}	Exactly n times	/a{3}/	"aaa"	"aa", "aaaa"
{n,}	n or more times	/a{2,}/	"aa", "aaa", "aaaaa"	"a"
{n,m}	Between n and m times (inclusive)	/a{1,3}/	"a", "aa", "aaa"	"aaaa"

Examples of curly brace quantifiers:

Example	Description	Matches	Does NOT Match
/go{2,4}d/	Matches "g", 2-4 "o"s, then "d"	"good", "goood", "gooood"	"god", "goooood"
/20{1,2}/	Matches a 2 followed by one to two zeroes	"20" "200"	"2" "2000"

3. Character Classes and Groups

3.1 Character Sets ([])

Character sets match any one of the characters enclosed within the square brackets.

Example	Description	Matches	Does NOT Match
/[abc]/	Matches "a", "b", or "c"	"a", "b", "c", "bat"	"d", "x", " "
/[aeiou]/	Matches any vowel (lowercase)	"a", "e", "i", "apple"	"b", "x", " "
/[0-9]/	Matches any digit (equivalent to \d - see below)	"0", "5", "9", "123"	"a", "!", " "
/[a-z]/	Matches any lowercase letter (a to z)	"a", "g", "z", "cat"	"A", "1", "!"
/[A-Za-z]/	Matches any uppercase or lowercase letter	"a", "G", "z", "Cat"	"1", "!", " "
/[0-9a-fA-F]/	Matches a character, any hexadecimal digit (case-insensitive)	"0", "a", "F", "B2"	"g", "X", " "

3.2 Negated Character Sets ([^])

Adding a caret (^) immediately after the opening bracket negates the set, meaning it matches any character except those within the brackets.

Example	Description	Matches	Does NOT Match
/[^abc]/	Matches any character except "a", "b", or "c"	"d", "x", " ", "1"	"a", "b", "c"
/[^0-9]/	Matches any character that is not a digit (like \D)	"a", "!", " "	"0", "5", "9"
/[^ \t\n]/	Matches anything that is not a space, a tab or a newline	"c", "d", "1"	" ", "\n", "\t"

3.3 Character Classes (Shorthands)

These are convenient shorthands for common character sets.

Class	Description	Equivalent Character Set	Matches	Does NOT Match
\d	Digit	[0-9]	"0", "5", "9"	"a", "!"
\D	Non-digit	[^0-9]	"a", "!", " "	"0", "5", "9"
\w	Word character (alphanumeric + underscore)	[a-zA-Z0-9_]	"a", "5", "_"	"!", " "
\W	Non-word character	[^a-zA-Z0-9_]	"!", " ", "-"	"a", "5", "_"
\s	Whitespace character (space, tab, newline, etc.)	[ \t\r\n\f\v]	" ", "\t", "\n"	"a", "1"
\S	Non-whitespace character	[^ \t\r\n\f\v]	"a", "1", "!"	" ", "\t", "\n"
.	Any character (except newline, usually)	(Almost everything)	"a", "!", "1"	(Newline)

3.4 Word Boundary (\b and \B)

\b matches a word boundary. This is a zero-width assertion, meaning it doesn't consume characters, but rather asserts a position.

Example	Description	Matches (bold)	Does NOT Match (no bold)
/\bcat\b/	Matches "cat" as a whole word	"cat", "a cat", " cat!"	"scatter", "bobcat"
/\bcat/	Matches "cat" at the beginning of a word	"catalog", "a cat", " cat!"	"scatter"
/cat\b/	Matches "cat" at the end of a word	"bobcat", "a cat", "!cat"	"catalog"
/\Bcat\B/	Matches "cat" not at a word boundary. \B is the opposite of \b.	scatter	"cat", "a cat", " cat!"
/\Bcat/	Matches cat when it is not the beginning of a word.	scatter	"cat", "a cat", " cat!"

4. Grouping and Alternation

4.1 Capturing Groups (...)

Parentheses create capturing groups. This has two main purposes:

1. Grouping: Apply quantifiers to a whole group, not just a single character.
2. Capturing: The matched text within the group can be accessed later (backreferences, or in programming languages).

Example	Description	Group 1 Contents (if matched)
/(ab)+/	Matches one or more repetitions of "ab"	"ab", "abab", etc.
/(\w+)\s(\w+)/	Matches two words separated by whitespace; captures each word as a separate group	First word, Second word
/(https?):\/\/(www\.\w+\.\w+)/	Captures the protocol http or https and the domain	"http", "https", and the domain like "www.example.com"

4.2 Non-Capturing Groups (?:...)

Sometimes you want to group, but don't need to capture the matched text. Use (?:...) for this. This improves performance slightly.

Example	Description	Group 1 Contents
/(?:https?):\/\/(www\.\w+\.\w+)/	Matches the same as above, but the protocol ("http://" or "https://") is not captured as a separate group.	The domain

4.3 Backreferences (\1, \2, etc.)

Backreferences refer to the text captured by a previous capturing group. \1 refers to the first group, \2 to the second, and so on.

Example	Description	Matches	Does NOT Match
/(a)(b)\1\2/	Matches "a", then "b", then "a" again (from group 1), then "b" again (from group 2).	"abab"	"abba", "abcd"
/(cat\|dog) is \1/	Matches a string where "cat" or "dog" is repeated, e.g. "cat is cat" or "dog is dog", with proper backreference	"cat is cat", "dog is dog"	"cat is dog"
<([a-z]+)>.+<\/\1>	Matches basic HTML tags. Captures tag name, then matches content and closing tag.	<p>text</p>, <b>bold</b>	<p>text</b>

4.4 Alternation (|)

The pipe symbol (|) acts like an "OR".

Example	Description	Matches	Does NOT Match
/cat\|dog/	Matches either "cat" or "dog"	"cat", "dog"	"bird", "catdog"
/(c\|d)at/	Matches either "cat" or "dat"	"cat", "dat"	"bat"
/gr(a\|e)y/	Matches "gray" or "grey"	"gray", "grey"	"graey"

5. Anchors

Anchors assert the position within the string, but don't consume characters (zero-width assertions).

Anchor	Description	Example	Matches (bold)	Does NOT Match (no bold)
^	Start of string (or line, in multiline mode)	/^Hello/	"Hello world"	"Say Hello"
$	End of string (or line, in multiline mode)	/world$/	"Hello world"	"world peace"
^$	Matches only an empty line	/^$/	"", "\n"	"a" " "

Example of combined start and end anchors:

Example	Description	Matches	Does NOT Match
/^Monday$/	Will match "Monday" but only as the only content on the string. This is useful for validation.	"Monday"	" Monday" or "Monday "

6. Flags (Modifiers)

Flags modify the behavior of the regex engine. They are typically placed after the closing slash of the regex.

Flag	Description	Example	Matches (without flag)	Matches (with flag)
g	Global: Find all matches, not just the first one.	/a/g	"banana"	"banana"
i	Case-insensitive: Ignore case when matching.	/hello/i	(no match)	"Hello", "hello"
m	Multiline: Treat ^ and $ as the start/end of each line (instead of the start/end of the entire string).	/^cat$/m	(no match)	"cat\ndog\ncat"
s	Dotall (Single-line): Makes the dot (.) match any character, including newline characters.	/a.b/s	(no match if a and b are on different lines)	"a\nb"
u	Unicode: Enable full Unicode support. Important for working with characters outside the basic ASCII range.	/\p{L}/u	(May not match all Unicode letters without u)	Matches all Unicode letters
y	Sticky: Matches only from the index indicated by the lastIndex property of this regular expression in the target string (and does not attempt to match from any later indexes).	/foo/y	"foobar"	(no match)