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Anchors
^: start of the string or the start of a line in a multiline pattern
$: end of the string or the end of a line in a multiline pattern
\b: word boundary
\B: not word boundary (opposite of \b)
Note: Anchors are non-quantifiable (i.e. cannot be followed by a quantifier).
Character sequences
.: any character except line breaks
\w: any word character
\W: any non-word character (opposite of \w)
\s: any whitespace character
\S: any non-whitespace character (opposite of \s)
\d: any digit character
\D: any non-digit character (opposite of \d)
[abc]: a single character in the given set (here a, b or c)
[^abc]: a single character not in the given set (opposite of [abc])
[a-z]: a single character in the given range (here between a and z inclusive)
[^a-z]: a single character not in the given range (opposite of [a-z])
[a-zA-Z]: a single character in either of the given ranges
Note: Use \ to escape special characters (e.g. \, /, [, ], (, ), {, } etc.).
Quantifiers
a?: zero or one of a (equal to a{0,1})
a*: zero or more of a (equal to a{0,})
a+: one or more of a (equal to a{1,})
a{3}: exactly 3 of a
a{3,}: 3 or more of a
a{3,5}: between 3 and 5 of a (inclusive)
Note: a is any valid quantifiable expression.
Groups
(ab): match and capture everything enclosed (here exactly ab)
(a|b): match and capture either one character (here a or b)
(?:ab): match everything enclosed, without capturing
Flags
g: Global
m: Multiline
i: Case insensitive
u: Unicode
Note that this cheatsheet is meant only as a starting point and is by no means a complete guide to all the features and nuances of regular expressions. You can also read for a deeper dive into some more advanced features.
