Package syntax parses regular expressions into parse trees and compiles
parse trees into programs. Most clients of regular expressions will use the
facilities of package [regexp] (such as [regexp.Compile] and [regexp.Match]) instead of this package.
The regular expression syntax understood by this package when parsing with the [Perl] flag is as follows.
Parts of the syntax can be disabled by passing alternate flags to [Parse].
Single characters:
. any character, possibly including newline (flag s=true) [xyz] character class [^xyz] negatedcharacterclass \dPerlcharacterclass \DnegatedPerlcharacterclass [[:alpha:]] ASCIIcharacterclass [[:^alpha:]] negatedASCIIcharacterclass \pNUnicodecharacterclass (one-lettername) \p{Greek} Unicode character class \PNnegatedUnicodecharacterclass (one-lettername) \P{Greek} negated Unicode character class
Composites:
xy x followed by y x|y x or y (prefer x)
Repetitions:
x* zero or more x, prefer more x+ one or more x, prefer more x? zero or one x, prefer one x{n,m} n or n+1 or ... or m x, prefer more x{n,} n or more x, prefer more x{n} exactly n x x*? zero or more x, prefer fewer x+? one or more x, prefer fewer x?? zero or one x, prefer zero x{n,m}? n or n+1 or ... or m x, prefer fewer x{n,}? n or more x, prefer fewer x{n}? exactly n x
Implementation restriction: The counting forms x{n,m}, x{n,}, and x{n}
reject forms that create a minimum or maximum repetition count above 1000.
Unlimited repetitions are not subject to this restriction.
Grouping:
(re) numbered capturing group (submatch) (?P<name>re) named & numbered capturing group (submatch) (?<name>re) named & numbered capturing group (submatch) (?:re) non-capturing group (?flags) set flags within current group; non-capturing (?flags:re) set flags during re; non-capturing
Flag syntax is xyz (set) or -xyz (clear) or xy-z (set xy, clear z). The flags are:
i case-insensitive (default false) m multi-line mode: ^ and $ match begin/end line in addition to begin/end text (default false) s let . match \n (default false) U ungreedy: swap meaning of x* and x*?, x+ and x+?, etc (default false)
Empty strings:
^ at beginning of text or line (flag m=true) $ at end oftext (like \z not \Z) or line (flag m=true) \A at beginning of text \b at ASCII word boundary (\w on one side and \W, \A, or \z on the other) \B not at ASCII word boundary \z at end of text
Escape sequences:
\a bell (== \007) \f form feed (== \014) \t horizontal tab (== \011) \n newline (== \012) \r carriage return (== \015) \v vertical tab character (== \013) \* literal *, for any punctuation character * \123 octal character code (up to three digits) \x7F hex character code (exactly two digits) \x{10FFFF} hex character code \Q...\E literal text ... even if... has punctuation
Character class elements:
x single character A-Z character range (inclusive) \d Perl character class [:foo:] ASCIIcharacterclassfoo \p{Foo} Unicode character classFoo \pFUnicodecharacterclassF (one-lettername)
Named character classes as character class elements:
[\d] digits (== \d) [^\d] not digits (== \D) [\D] not digits (== \D) [^\D] not not digits (== \d) [[:name:]] named ASCIIclassinsidecharacterclass (== [:name:]) [^[:name:]] namedASCIIclassinsidenegatedcharacterclass (== [:^name:]) [\p{Name}] named Unicode property inside character class (== \p{Name}) [^\p{Name}] named Unicode property inside negated character class (== \P{Name})
Perl character classes (all ASCII-only):
\d digits (== [0-9]) \D not digits (== [^0-9]) \s whitespace (== [\t\n\f\r ]) \S not whitespace (== [^\t\n\f\r ]) \w word characters (== [0-9A-Za-z_]) \W not word characters (== [^0-9A-Za-z_])
Package syntax parses regular expressions into parse trees and compiles parse trees into programs. Most clients of regular expressions will use the facilities of package [regexp] (such as [regexp.Compile] and [regexp.Match]) instead of this package.
Syntax
The regular expression syntax understood by this package when parsing with the [Perl] flag is as follows. Parts of the syntax can be disabled by passing alternate flags to [Parse].
Single characters:
Composites:
Repetitions:
Implementation restriction: The counting forms x{n,m}, x{n,}, and x{n} reject forms that create a minimum or maximum repetition count above 1000. Unlimited repetitions are not subject to this restriction.
Grouping:
Empty strings:
Escape sequences:
Character class elements:
Named character classes as character class elements:
Perl character classes (all ASCII-only):
ASCII character classes:
Unicode character classes are those in [unicode.Categories] and [unicode.Scripts].