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   pcrepattern    ( 3 )

Perl-совместимые регулярные выражения (Perl-compatible regular expressions)
  Name  |  Pcre regular expression details  |  Special start-of-pattern items  |  Ebcdic character codes  |  Characters and metacharacters  |  Backslash  |  Circumflex and dollar  |  Full stop (period, dot) and \n  |  Matching a single data unit  |  Square brackets and character classes  |  Posix character classes  |  Compatibility feature for word boundaries  |  Vertical bar  |  Internal option setting  |  Subpatterns  |  Duplicate subpattern numbers  |  Named subpatterns  |  Repetition  |  Atomic grouping and possessive quantifiers  |  Back references  |  Assertions  |  Conditional subpatterns  |  Comments  |  Recursive patterns  |  Subpatterns as subroutines  |    Oniguruma subroutine syntax    |  Callouts  |  Backtracking control  |  See also  |

ONIGURUMA SUBROUTINE SYNTAX

For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or a number enclosed either in angle brackets or single quotes, is an alternative syntax for referencing a subpattern as a subroutine, possibly recursively. Here are two of the examples used above, rewritten using this syntax:

(?<pn> \( ( (?>[^()]+) | \g<pn> )* \) ) (sens|respons)e and \g'1'ibility

PCRE supports an extension to Oniguruma: if a number is preceded by a plus or a minus sign it is taken as a relative reference. For example:

(abc)(?i:\g<-1>)

Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not synonymous. The former is a back reference; the latter is a subroutine call.