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Characters

x The character x
\\ The backslash character
\0n The character with octal value 0n (0 <= n <= 7)
\0nn The character with octal value 0nn (0 <= n <= 7)
\0mnn The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh The character with hexadecimal value 0xhh
\uhhhh The character with hexadecimal value 0xhhhh
\x{h..h} The character with hexadecimal value 0xh...h
\t The tab character ('\u0009')
\n The newline (line feed) character ('\u000A')
\r The carriage-return character ('\u000D')
\f The form-feed character ('\u000C')
\a The alert (bell) character ('\u0007')
\e The escape character ('\u001B')
\cx The control character corresponding to x

Character classes

[abc] a, b, or c (simple class)
[^abc] Any character except a, b, or c (negation)
[a-zA-Z] a through z or A through Z, inclusive (range)
[a-d[m-p]] a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]] d, e, or f (intersection)
[a-z&&[^bc]] a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]] a through z, and not m through p: [a-lq-z] (subtraction)

Predefined character classes

. Any character (may or may not match line terminators)
\X Single grapheme - equivalent to (?>\P{M}\p{M}*)
\d A digit: [0-9]
\D A non-digit: [^0-9]
\h A horizontal whitespace character: [ \t\xA0\u1680\u180e\u2000-\u200a\u202f\u205f\u3000]
\H A non-horizontal whitespace character: [^\h]
\s A whitespace character: [ \t\n\x0B\f\r]
\S A non-whitespace character: [^\s]
\v A vertical whitespace character: [\n\x0B\f\r\x85\u2028\u2029]
\V A non-vertical whitespace character: [^\v]
\w A word character: [a-zA-Z_0-9]
\W A non-word character: [^\w]

POSIX character classes (US-ASCII only)

For more details, see the page on POSIX character classes

\p{Lower} A lower-case alphabetic character: [a-z]
\p{Upper} An upper-case alphabetic character: [A-Z]
\p{ASCII} All ASCII: [\x00-\x7F]
\p{Alpha} An alphabetic character: [\p{Lower}\p{Upper}]
\p{Digit} A decimal digit: [0-9]
\p{Alnum} An alphanumeric character: [\p{Alpha}\p{Digit}]
\p{Punct} Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
\p{Graph} A visible character: [\p{Alnum}\p{Punct}]
\p{Print} A printable character: [\p{Graph}\x20]
\p{Blank} A space or a tab: [ \t]
\p{Cntrl} A control character: [\x00-\x1F\x7F]
\p{XDigit} A hexadecimal digit: [0-9a-fA-F]
\p{Space} A whitespace character: [ \t\n\x0B\f\r]

POSIX character classes (US-ASCII only)

Equivalent to the above POSIX classes - only allowed in a character class

For more details, see the page on POSIX character classes

[:lower:] A lower-case alphabetic character: [a-z]
[:upper:] An upper-case alphabetic character: [A-Z]
[:ascii:] All ASCII: [\x00-\x7F]
[:alpha:] An alphabetic character: [[:lower:][:upper:]]
[:digit:] A decimal digit: [0-9]
[:alnum:] An alphanumeric character: [[:alpha:][:digit:]]
[:punct:] Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
[:graph:] A visible character: [[:alnum:][:punct:]]
[:print:] A printable character: [[:graph:]\x20]
[:blank:] A space or a tab: [ \t]
[:cntrl:] A control character: [\x00-\x1F\x7F]
[:xdigit:] A hexadecimal digit: [0-9a-fA-F]
[:space:] A whitespace character: [ \t\n\x0B\f\r]
[:word:] A word character: [\w]

java.lang.Character classes (simple java character type)

\p{javaLowerCase} Equivalent to java.lang.Character.isLowerCase()
\p{javaUpperCase} Equivalent to java.lang.Character.isUpperCase()
\p{javaWhitespace} Equivalent to java.lang.Character.isWhitespace()
\p{javaMirrored} Equivalent to java.lang.Character.isMirrored()

Classes for Unicode blocks and categories

\p{InGreek} A character in the Greek block (simple block)
\p{Lu} An uppercase letter (simple category)
\p{Sc} A currency symbol
\P{InGreek} Any character except one in the Greek block (negation)
[\p{L}&&[^\p{Lu}]] Any letter except an uppercase letter (subtraction)

Boundary matchers

^ The beginning of a line
$ The end of a line
\b A word boundary
\B A non-word boundary
\A The beginning of the input
\G The end of the previous match
\Z The end of the input but for the final terminator, if any
\z The end of the input

Greedy quantifiers

X? X, once or not at all
X* X, zero or more times
X+ X, one or more times
X{n} X, exactly n times
X{n,} X, at least n times
X{n,m} X, at least n but not more than m times

Reluctant quantifiers

X?? X, once or not at all
X*? X, zero or more times
X+? X, one or more times
X{n}? X, exactly n times
X{n,}? X, at least n times
X{n,m}? X, at least n but not more than m times

Possessive quantifiers

X?+ X, once or not at all
X*+ X, zero or more times
X++ X, one or more times
X{n}+ X, exactly n times
X{n,}+ X, at least n times
X{n,m}+ X, at least n but not more than m times

Logical operators

XY X followed by Y
X|Y Either X or Y

Capturing

(X) X, as a capturing group
(?<name>X) X, as a named-capturing group
(?'name'X) X, as a named-capturing group
(?P<name>X) X, as a named-capturing group

Back references

For more details, see the page on back references

\n Whatever the n^th capturing group matched
\gn Whatever the n^th capturing group matched
\g{n} Whatever the n^th capturing group matched
\g-n Relative back reference
\g{-n} Relative back reference
\k<name> Whatever the named-capturing group "name" matched
\k'name' Whatever the named-capturing group "name" matched
\g{name} Whatever the named-capturing group "name" matched
\k{name} Whatever the named-capturing group "name" matched
(?P=name) Whatever the named-capturing group "name" matched

Quotation

\ Matches nothing, but quotes the following character
\Q Matches nothing, but quotes all characters until \E
\E Matches nothing, but ends quoting started by \Q

Special constructs (non-capturing)

(?:X) X, as a non-capturing group
(?idmsuxJn-idmsuxJn) Matches nothing, but turns match flags i d m s u x J n on - off
(?idmsuxJn-idmsuxJn:X) X, as a non-capturing group with the given flags i d m s u x J n on - off
(?>X) X, as an independent (atomic), non-capturing group
(?|X) X, as a "branch reset" pattern

Assertions (non-capturing)

(?=X) X, via zero-width positive lookahead
(?!X) X, via zero-width negative lookahead
(?<=X) X, via zero-width positive lookbehind
(?<!X) X, via zero-width negative lookbehind

Comment (non-capturing)

(?x:#comment\n) comment (cannot contain a line terminator)
(?xd:#comment\n) comment (cannot contain '\n')
(?#comment) comment (cannot contain a close parenthesis)

Conditional patterns (non-capturing)

For more details, see the page on conditionals

(?(condition)yes-pattern) (?(condition)yes-pattern|no-pattern)

(?(n)...) absolute reference condition
(?(-n)...) relative reference condition
(?(<name>)...) named reference condition
(?('name')...) named reference condition
(?(name)...) named reference condition
(?(assert)...) assert condition

Numeric ranges (non-capturing)

For more details, see the page on numeric ranges

(?Z[start..end]) matches a numeric range (allowing for leading zeros)
(?Z16[start..end]) matches a numeric range in base 16 (allowing for leading zeros)
(?NZ[start..end]) matches a numeric range (not allowing for leading zeros)
(?NZ16[start..end]) matches a numeric range in base 16 (not allowing for leading zeros)