正则表达式模式解释

Question

我对正则表达式相当陌生，最近我偶然发现了 perl 脚本中的正则表达式，但我无法弄清楚：

$groups= qr/\(([^()]+|(??{$groups}))*\)/;

任何帮助将不胜感激！

Answer 1

好吧，如果你扩展它：

$groups= qr/
  \(                 # match an open paren (
    (                # followed by
      [^()]+         # one or more non-paren character
    |                # OR
      (??{$groups})  # the regex itself
    )*               # repeated zero or more times
  \)                 # followed by a close paren )
/x;

你会得到一个优雅的递归方法来找到平衡的括号:)

Answer 2

YAPE::Regex::Explain 模块可以告诉您什么正则表达式正在做：

% perl5.14.2 -MYAPE::Regex::Explain -E 'say YAPE::Regex::Explain->new(shift)->explain' '\(([^()]+|(??{$groups}))*\)'
The regular expression:

(?-imsx:\(([^()]+|(??{$groups}))*\))

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  \(                       '('
----------------------------------------------------------------------
  (                        group and capture to \1 (0 or more times
                           (matching the most amount possible)):
----------------------------------------------------------------------
    [^()]+                   any character except: '(', ')' (1 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    (??{$groups})            run this block of Perl code (that isn't
                             interpolated until RIGHT NOW)
----------------------------------------------------------------------
  )*                       end of \1 (NOTE: because you are using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \1)
----------------------------------------------------------------------
  \)                       ')'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

您可以将该单行代码转换为您的个人资料中的别名：

alias re="perl -MYAPE::Regex::Explain -E 'say YAPE::Regex::Explain->new(shift)->explain'"

之后，您不必记住所有这些：

re '\(([^()]+|(??{$groups}))*\)'