Regex 与perl兼容的正则表达式能否比较两个数字？

定位本杰明按钮

鉴于

Born,Died
1852,1891
1862,1862
1902,1785

..，在perl兼容的正则表达式中是否有与第四行匹配的语法，其中第一个值大于第二个值

我猜是某种结合

(\d+),(\d+)

。。。而且

(??{$1>$2})

..，但这可能是不可能的，因为正则表达式是词法的，匹配是算术的

编辑：由于环境接受pcre模式，但禁止使用perl程序，因此这被限制为pcre正则表达式。

Summary 此正则表达式假定源代码是4位字符串。它将查找第一个逗号分隔的数字大于第二个数字的实例。
如本文所述，此正则表达式假定您使用的是忽略空白或换行符的“x”标志

正则表达式 样本采集 简短解释 正则表达式的开头有一个前瞻性，以验证我们确实有两个4位数字

四个代码块测试每个位置，以验证一个数字是否大于另一个数字。第二、第三和第四个块包含命名的反向引用（分别为a、b和c）。此反向参考确保前导数字相同

更详细的解释

---

使用Perl“延迟执行断言”（？{code}））的工作模式是：

^(\d{4}),(\d{4})(??{ $1 > $2 ? "" : "(?!)"})$

延迟执行断言将代码返回的值放入正则表达式中。这种情况下的效果是，如果第一个数字大于第二个数字（因此它匹配），则模式变为

^（\d{4}），（\d{4}）$

，否则变为

^（\d{4}），（\d{4}）（？！）$

（？！）

是一个否定的前瞻断言，它从不匹配，因为Perl认为空模式总是匹配的

Perl中的另一个选项是使用“条件表达式”

（？（条件）yes模式）

，以及“代码求值断言”

（？{code}）

：

这将尝试查找具有相同前缀的数字对，并且第二个数字中的第一个不同字符不是非数字（即，它是一个数字），并且不等于或大于第一个数字中的相应数字（即，它小于另一个数字）。不幸的是，它不起作用。原因已在中解释。基本上，反向引用在角色类中不起作用。这个想法可以通过使用延迟执行断言（

^（\d*）（\d）\d*，\1（？{{2}-9]}）\d*$

）来实现，但这对PCRE仍然没有好处

一个与PCRE兼容的选项是使用强力版本的检查第一个不同的数字。查找1后跟0，或2后跟0或1，或3后跟0或1或2。这段Bash代码生成正则表达式：

regex='^(?=\d{4},\d{4}$)'   # Match only lines of the form 'dddd,dddd'
regex+='(\d*)'              # Prefix of both numbers
regex+='(1\d*,\1[0]'        # 1 (followed by digits+','+prefix) followed by 0
for (( i=2 ; i<=9 ; i++ )) ; do
    regex+="|$i\d*,\1[0-$((i-1))]"  # or $i (...) followed by a lesser digit
done
regex+=')\d*$'
printf '%s\n' "$regex"

---

正如@ThisSuiteisBlack在评论中所指出的，正则表达式并不是最好的方法。另请参见。

为了澄清，您是要Perl正则表达式还是PCRE正则表达式。另外，在Perl中，如果没有正则表达式（并且更易于阅读），这是一件微不足道的事情：

while（）{chomp；my（$born，$died）=split/，/；print if$died<$born；}

是否有什么理由必须使用正则表达式？@thisSuitesBlacknot，我个人对{code}的语法很好奇，但手头的问题需要PCRE。根据你提供的链接，手头的问题是没有希望的；除非pcre调出功能可能是一个桥梁。现在，这是一个答案，但很酷的regex魔术：

perl-le'$x=“123456”；打印$x=~/（\d），（[\1-9]）/；打印$1；打印$2；'-只要你处理的是1位数的数字，正则表达式就可以完成你的工作。那怎么办？
[0][0] = 1902,1785
[0][a] = 1
[0][b] = 
[0][c] = 
[1][0] = 1111,1110
[1][a] = 
[1][b] = 
[1][c] = 111
[2][0] = 2222,2202
[2][a] = 
[2][b] = 22
[2][c] = 
[3][0] = 3333,3033
[3][a] = 3
[3][b] = 
[3][c] = 
[4][0] = 4444,0444
[4][a] = 
[4][b] = 
[4][c] = 
[5][0] = 4567,1234
[5][a] = 
[5][b] = 
[5][c] = 

NODE                     EXPLANATION
----------------------------------------------------------------------
  ^                        the beginning of a "line"
----------------------------------------------------------------------
  (?=                      look ahead to see if there is:
----------------------------------------------------------------------
    \d{4}                    digits (0-9) (4 times)
----------------------------------------------------------------------
    ,                        ','
----------------------------------------------------------------------
    \d{4}                    digits (0-9) (4 times)
----------------------------------------------------------------------
    (?:                      group, but do not capture:
----------------------------------------------------------------------
      \D                       non-digits (all but 0-9)
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      \Z                       before an optional \n, and the end of
                               the string
----------------------------------------------------------------------
    )                        end of grouping
----------------------------------------------------------------------
  )                        end of look-ahead
----------------------------------------------------------------------
  (?:                      group, but do not capture:
----------------------------------------------------------------------
    (?:                      group, but do not capture:
----------------------------------------------------------------------
      [9]                      any character of: '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [012345678]              any character of: '0', '1', '2', '3',
                               '4', '5', '6', '7', '8'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      [89]                     any character of: '8', '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [01234567]               any character of: '0', '1', '2', '3',
                               '4', '5', '6', '7'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      [789]                    any character of: '7', '8', '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [0123456]                any character of: '0', '1', '2', '3',
                               '4', '5', '6'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      [6789]                   any character of: '6', '7', '8', '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [012345]                 any character of: '0', '1', '2', '3',
                               '4', '5'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      [56789]                  any character of: '5', '6', '7', '8',
                               '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [01234]                  any character of: '0', '1', '2', '3',
                               '4'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      [456789]                 any character of: '4', '5', '6', '7',
                               '8', '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [0123]                   any character of: '0', '1', '2', '3'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      [3456789]                any character of: '3', '4', '5', '6',
                               '7', '8', '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [012]                    any character of: '0', '1', '2'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      [23456789]               any character of: '2', '3', '4', '5',
                               '6', '7', '8', '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [01]                     any character of: '0', '1'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      [123456789]              any character of: '1', '2', '3', '4',
                               '5', '6', '7', '8', '9'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      ,                        ','
----------------------------------------------------------------------
      [0]                      any character of: '0'
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
    )                        end of grouping
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
  )                        end of grouping
----------------------------------------------------------------------
)                        end of grouping

^(\d{4}),(\d{4})(??{ $1 > $2 ? "" : "(?!)"})$

^(\d{4}),(\d{4})(?(?{ $1 <= $2 })(?!))$

^(\d*)(\d)\d*,\1[^\D\2-9]\d*$

regex='^(?=\d{4},\d{4}$)'   # Match only lines of the form 'dddd,dddd'
regex+='(\d*)'              # Prefix of both numbers
regex+='(1\d*,\1[0]'        # 1 (followed by digits+','+prefix) followed by 0
for (( i=2 ; i<=9 ; i++ )) ; do
    regex+="|$i\d*,\1[0-$((i-1))]"  # or $i (...) followed by a lesser digit
done
regex+=')\d*$'
printf '%s\n' "$regex"

^(?=\d{4},\d{4}$)(\d*)(1\d*,\1[0]|2\d*,\1[0-1]|3\d*,\1[0-2]|4\d*,\1[0-3]|5\d*,\1[0-4]|6\d*,\1[0-5]|7\d*,\1[0-6]|8\d*,\1[0-7]|9\d*,\1[0-8])\d*$