Regular Expressions Cheatsheet

Basic Classes: Playing with characters

Symbol	Description	Example
.	Matches any single character except newline.	c.t matches cat, cut, cot, etc.
*	Matches zero or more occurrences of the preceding character.	ab*c matches ac, abc, abbc, abbbc, etc.
+	Matches one or more occurrences of the preceding character.	ab+c matches abc, abbc, abbbc, etc.
?	Matches zero or one occurrence of the preceding character.	colou?r matches color or colour.
^	Matches the beginning of a line.	^hello matches hello at the beginning of a line.
$	Matches the end of a line.	world$ matches world at the end of a line.
[]	Matches any one of the enclosed characters.	[abc] matches a, b, or c.
[a-z]	Matches any character between a and z.	[a-z]+ matches any lowercase word.
[^]	Matches any character not enclosed in the brackets.	[^abc] matches any character except a, b, or c.
()	Groups multiple tokens together and creates a capture group.	([0-9]{3})-([0-9]{4}) matches a phone number in the format 123-4567 and captures the area code and number.
\	Escapes a special character.	\. matches a period.
\d	Matches any digit character. Equivalent to [0-9].	\d{3} matches any three digits.
\w	Matches any word character. Equivalent to [a-zA-Z0-9_].	\w+ matches any word.
\s	Matches any whitespace character. Equivalent to [ \t\n\r\f\v].	\s+ matches any whitespace.

Advanced Regex Concepts

Concept	Symbol	Explanation
Quantifiers	{n}<br>{n,m}<br>*<br>+<br>?	Quantifiers specify how many times a pattern should match. {n} specifies an exact number of matches, {n,m} specifies a range of matches, * specifies zero or more matches, + specifies one or more matches, and ? specifies zero or one match.
Alternation	`	`
Grouping	()	Grouping allows you to create subexpressions within a regular expression. This can be useful for applying quantifiers or alternation to multiple characters at once. For example, (abc)+ matches one or more repetitions of the sequence "abc".
Backreferences	\1, \2, etc.	Backreferences allow you to refer to a previously matched group within a regular expression. For example, (\w+) \1 matches repeated words like "hello hello" or "cat cat".
Lookahead and Lookbehind	(?=...), (?!...), (?<=...), (?<!...)	Lookahead and lookbehind are zero-width assertions that allow you to check for patterns before or after the current position in the string, without actually consuming any characters. Positive lookahead ((?=...)) matches if the pattern inside the lookahead matches, negative lookahead ((?!...)) matches if the pattern inside the lookahead does not match, positive lookbehind ((?<=...)) matches if the pattern inside the lookbehind matches behind the current position, and negative lookbehind ((?<!...)) matches if the pattern inside the lookbehind does not match behind the current position.