Question

如果正则表达式是例如^(?<object>[\-\w]+)/([\-\w]+)$，会将第二个捕获组调用为$2还是$1？换句话说，匿名捕获组是绝对的还是相对编号的？

Answer 1

使用$2引用第二个编号捕获组。请注意，我不会将其称为匿名，也许，“未命名”会更适合这里。

查看sample regex demo。

请参阅PCRE docs：

PCRE支持使用命名和编号的捕获括号。名称只是识别括号的另一种方法，它仍然可以获取数字。

Answer 2

在PCRE中，捕获组按找到的顺序按顺序编号。

这是一个示例，其中组被注释，缩进和编号（与一些条件混合）。

     # ==============================
     # Variations of the same thing
     # ==============================

1    ( a )?
2    ( b )?
3    ( c )?
c    (?(1)
       |  
   c      (?(2)
            |  
      c        (?(3) | (*FAIL) )
          )
     )

     # ==============================

4    (
  5       ( a )?
  6       ( b )?
  7       ( c )?
4    )
c    (?(2)
       |  
   c      (?(3)
            |  
      c        (?(4) | (*FAIL) )
          )
     )

     # ==============================

8    (?<A> a )?
9    (?<B> b )?
10   (?<C> c )?
c    (?(<A>)
       |  
   c      (?(<B>)
            |  
      c        (?(<C>) | (*FAIL) )
          )
     )

     # ==============================

11   (?<M>
  12      (?<A> a )?
  13      (?<B> b )?
  14      (?<C> c )?
c         (?(<A>)
            |  
   c           (?(<B>)
                 |  
      c             (?(<C>) | (*FAIL) )
               )
          )
11   )

     # ==============================

分支重置稍微区别对待条件在BR开始的下一个组号处，它按顺序编号在每个分支的开头。
经过BR后，编号在分配的最大计数后开始1+ 来自一个分支。

示例：

     # Super Branch with Conditional's

1    ( a )                     # (1)
     (?|
          x
br 2      ( y )                     # (2)
          z
          (?|
   br 3        ( u )                     # (3)
      4        ( u )                     # (4)
c              (?(1)
      5             ( R )                     # (5)
                 |  (?|
      br 6               ( x )                     # (6)
                      |  
      br 6               ( x )                     # (6)
   c                     (?(2)
                              a
                           |  
         7                    ( b )                     # (7)
                         )
         8               ( c )                     # (8)
                    )
               )
      9        ( u )                     # (9)
      10       ( u )                     # (10)
            |  
   br 3        ( e )                     # (3)
      4        ( e )                     # (4)
      5        ( e )                     # (5)
            |  
   br 3        ( c )                     # (3)
          )
   11     ( K )                     # (11)
       |  
br 2      (                         # (2 start)
               p
     3         (                         # (3 start)
                    q
                    (?|
       br 4              ( M )                     # (4)
          5              ( M )                     # (5)
          6              ( M )                     # (6)
          7              ( M )                     # (7)
                         (?|
          br 8                ( T )                     # (8)
             9                ( T )                     # (9)
             10               ( T )                     # (10)
                           |  
          br 8                ( D )                     # (8)
             9                ( D )                     # (9)
                         )
          12             ( R )                     # (12)
          13             ( R )                     # (13)
                      |  
       br 4              ( B )                     # (4)
          5              ( B )                     # (5)
          6              ( B )                     # (6)
                      |  
       br 4              ( v )                     # (4)
                    )
     3         )                         # (3 end)
               r
   2      )                         # (2 end)
   14     ( o )                     # (14)
   15     ( i )                     # (15)
       |  
br 2      ( t )                     # (2)
          s
   3      ( w )                     # (3)
     )
16   ( Z )                     # (16)

Dot-Net计数附录

有两种计算Dot-Net捕获的选项。

计算名为捕获组
命名组最后

显然，如果没有1，你就不会得到2.

示例：不计算命名组

1    (                             # (1 start)
          (?'overall'
               ^
               (?= [^&] )
               (?:
                    (?<scheme> [^:/?#]+ )
                    :
               )?
               (?:
                    //
  2                 ( )                           # (2)
                    (?<authority> [^/?#]* )
               )?
               (?<path> [^?#]* )
               (?:
                    \?
                    (?<query> [^#]* )
               )?
  3            ( )                           # (3)
               (?:
                    \#
                    (?<fragment> .* )
               )?
          )
1    )                             # (1 end)

示例：计算命名组

1    (                             # (1 start)
  2       (?'overall'                   # (2 start)
               ^
               (?= [^&] )
               (?:
    3               (?<scheme> [^:/?#]+ )         # (3)
                    :
               )?
               (?:
                    //
    4               ( )                           # (4)
    5               (?<authority> [^/?#]* )       # (5)
               )?
    6          (?<path> [^?#]* )             # (6)
               (?:
                    \?
    7               (?<query> [^#]* )             # (7)
               )?
    8          ( )                           # (8)
               (?:
                    \#
    9               (?<fragment> .* )             # (9)
               )?
  2       )                             # (2 end)
1    )                             # (1 end)

示例：计算命名组，命名组最后

1    (                             # (1 start)
  4       (?'overall'                   #_(4 start)         
               ^
               (?= [^&] )
               (?:
    5               (?<scheme> [^:/?#]+ )         #_(5)         
                    :
               )?
               (?:
                    //
    2               ( )                           # (2)
    6               (?<authority> [^/?#]* )       #_(6)         
               )?
    7          (?<path> [^?#]* )             #_(7)         
               (?:
                    \?
    8               (?<query> [^#]* )             #_(8)         
               )?
    3          ( )                           # (3)
               (?:
                    \#
    9               (?<fragment> .* )             #_(9)         
               )?
  4       )                             #_(4 end)         
1    )                             # (1 end)

命名和未命名的PCRE捕获组如何交互？

2 个答案: