这个正则表达式在做什么？

Question

/^([a-z]:)?\//i

?如果我必须从我理解的内容中解释它,我不太明白这个正则表达式是什么:

匹配开始"Group1是a到z和:"外部?(我不知道它做什么)\/使得它匹配/并且选项/i"不区分大小写".

我意识到这将返回0或1不安静确定为什么因为 ?

这是匹配目录路径还是什么？

如果我测试它:

$var = 'test'得到0而$var ='/test';得到1但$var = 'test/'得到0

所以任何开头/都会得到1和其他任何东西0.

有人可以用基本的术语向我解释这个正则表达式吗？

Answer 1

请参阅YAPE :: Regex :: Explain:

#!/usr/bin/perl

use strict; use warnings;

use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(qr/^([a-z]:)?\//i)->explain;

The regular expression:

(?i-msx:^([a-z]:)?/)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?i-msx:                 group, but do not capture (case-insensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (                        group and capture to \1 (optional
                           (matching the most amount possible)):
----------------------------------------------------------------------
    [a-z]                    any character of: 'a' to 'z'
----------------------------------------------------------------------
    :                        ':'
----------------------------------------------------------------------
  )?                       end of \1 (NOTE: because you're using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \1)
----------------------------------------------------------------------
  /                        '/'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

Answer 2

它匹配一个小写或大写字母([a-z]带i修饰符),位于输入字符串(^)的开头,后跟冒号(:)全部可选(?),后跟正斜杠\/.

简而言之:

^          # match the beginning of the input
(          # start capture group 1
  [a-z]    #   match any character from the set {'A'..'Z', 'a'..'z'} (with the i-modifier!)
  :        #   match the character ':'
)?         # end capture group 1 and match it once or none at all
\/         # match the character '/'

Answer 3

? 将匹配前一个模式中的一个或不匹配.

?      Match 1 or 0 times

另见:perldoc perlre

说明:

/.../i   # case insensitive

^(...)   # match at the beginning of the string

[a-z]:   # one character between 'a' and 'z' followed by a colon

(...)?   # zero or one time of the group, enclosed in ()

所以在英语中:匹配任何以/(斜杠)或某个字母开头,后跟冒号后跟a的东西/.这看起来像是在unix和windows中匹配路径名,例如它匹配:

/home/user

和

C:/Applications

等等