这个Perl正则表达式意味着什么:m /(.*?):(.*?)$/ g？

Question

我正在编辑Perl文件,但我不理解这个正则表达式比较.有人可以向我解释一下吗？

if ($lines =~ m/(.*?):(.*?)$/g) { } .. 

这里发生了什么？$lines是文本文件中的一行.

Answer 1

将其分解为多个部分:

$lines =~ m/ (.*?)      # Match any character (except newlines)
                        # zero or more times, not greedily, and
                        # stick the results in $1.
             :          # Match a colon.
             (.*?)      # Match any character (except newlines)
                        # zero or more times, not greedily, and
                        # stick the results in $2.
             $          # Match the end of the line.
           /gx;

因此,这将匹配字符串":"(它匹配零个字符,然后是冒号,然后是行结尾前的零个字符,$1并且$2是空字符串),或者"abc:"($1 = "abc",$2是一个空字符串),或"abc:def:ghi"($1 = "abc"和$2 = "def:ghi").

如果你传入一个不匹配的行(看起来这将是字符串不包含冒号),那么它将不会处理括号内的代码.但如果它匹配,则括号内的代码可以使用和处理特殊$1和$2变量(至少,直到下一个正则表达式出现,如果括号内有一个).

Answer 2

有一个工具可以帮助理解正则表达式:YAPE :: Regex :: Explain.

忽略g修改器,这里不需要:

use strict;
use warnings;
use YAPE::Regex::Explain;

my $re = qr/(.*?):(.*?)$/;
print YAPE::Regex::Explain->new($re)->explain();

__END__

The regular expression:

(?-imsx:(.*?):(.*?)$)

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:
----------------------------------------------------------------------
    .*?                      any character except \n (0 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  :                        ':'
----------------------------------------------------------------------
  (                        group and capture to \2:
----------------------------------------------------------------------
    .*?                      any character except \n (0 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
  )                        end of \2
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

另见perldoc perlre.