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Summary of regular-expression constructs


xThe character x
\\The backslash character
\0nThe character with octal value 0n (0 <= n <= 7)
\0nnThe character with octal value 0nn (0 <= n <= 7)
\0mnnThe character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhhThe character with hexadecimal value 0xhh
\uhhhhThe character with hexadecimal value 0xhhhh
\tThe tab character ('\u0009')
\nThe newline (line feed) character ('\u000A')
\rThe carriage-return character ('\u000D')
\fThe form-feed character ('\u000C')
\aThe alert (bell) character ('\u0007')
\eThe escape character ('\u001B')
\cxThe 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)
\dA digit: [0-9]
\DA non-digit: [^0-9]
\sA whitespace character: [ \t\n\x0B\f\r]
\SA non-whitespace character: [^\s]
\wA word character: [a-zA-Z_0-9]
\WA non-word character: [^\w]

Boundary matchers

^The beginning of a line
$The end of a line
\bA word boundary
\BA non-word boundary
\AThe beginning of the input
\GThe end of the previous match
\zThe 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

XYX followed by Y
X|YEither X or Y
(X)X, as a capturing group

Back references

\nWhatever the nth capturing group matched


\Nothing, but quotes the following character
\QNothing, but quotes all characters until \E
\ENothing, but ends quoting started by \Q

Special constructs (non-capturing)

(?:X)X, as a non-capturing group
(?idmsux-idmsux) Nothing, but turns match flags i d m s u x on - off
(?idmsux-idmsux:X)  X, as a non-capturing group with the given flags i d m s u x on - off
(?=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
(?>X)X, as an independent, non-capturing group

Backslashes, escapes, and quoting

Line terminators

A line terminator is a one- or two-character sequence that marks the end of a line of the input character sequence. The following are recognized as line terminators:

  • A newline (line feed) character ('\n'),
  • A carriage-return character followed immediately by a newline character ("\r\n"),
  • A standalone carriage-return character ('\r'),
  • A next-line character ('\u0085'),
  • A line-separator character ('\u2028'), or
  • A paragraph-separator character ('\u2029).

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