正则表达式：多行，非贪婪匹配，直到可选字符串答案

【问题标题】：regexp: multiline, non-greedy match until optional string正则表达式：多行，非贪婪匹配，直到可选字符串
【发布时间】：2021-09-07 11:18:30
【问题描述】：

使用 Go 的正则表达式，我试图从原始文本中提取一组预定义的有序键值（多行）对，其最后一个元素可能是可选的，例如，

 Key1:
  SomeValue1
  MoreValue1
 Key2:
  SomeValue2
  MoreValue2
 OptionalKey3:
  SomeValue3
  MoreValue3

（这里，我想将所有值提取为命名组）

如果我使用默认的贪婪模式(?s:Key1:\n(?P<Key1>.*)Key2:\n(?P<Key2>.*)(?:OptionalKey3:\n(?P<OptionalKey3>.*))?)，它永远不会看到 OptionalKey3 并将其余文本匹配为 Key2。

如果我使用非贪婪模式(?s:Key1:\n(?P<Key1>.*)Key2:\n(?P<Key2>.*?)(?:OptionalKey3:\n(?P<OptionalKey3>.*))?)，它甚至看不到 SomeValue2 并立即停止：https://regex101.com/r/QE2g3o/1

有没有一种方法可以选择性地匹配 OptionalKey3，同时还能捕获所有其他的？

【问题讨论】：

标签： regex go re2

【解决方案1】：

使用

(?s)\AKey1:\n(?P<Key1>.*)Key2:\n(?P<Key2>.*?)(?:OptionalKey3:\n(?P<OptionalKey3>.*))?\z

见regex proof。

解释

--------------------------------------------------------------------------------
  (?s)                     set flags for this block (with . matching
                           \n) (case-sensitive) (with ^ and $
                           matching normally) (matching whitespace
                           and # normally)
--------------------------------------------------------------------------------
  \A                       the beginning of the string
--------------------------------------------------------------------------------
  Key1:                    'Key1:'
--------------------------------------------------------------------------------
  \n                       '\n' (newline)
--------------------------------------------------------------------------------
  (?P<Key1>                 group and capture to "Key1":
--------------------------------------------------------------------------------
    .*                       any character (0 or more times (matching
                             the most amount possible))
--------------------------------------------------------------------------------
  )                        end of "Key1"
--------------------------------------------------------------------------------
  Key2:                    'Key2:'
--------------------------------------------------------------------------------
  \n                       '\n' (newline)
--------------------------------------------------------------------------------
  (?P<Key2>                group and capture to "Key2":
--------------------------------------------------------------------------------
    .*?                      any character (0 or more times (matching
                             the least amount possible))
--------------------------------------------------------------------------------
  )                        end of "Key2"
--------------------------------------------------------------------------------
  (?:                      group, but do not capture (optional
                           (matching the most amount possible)):
--------------------------------------------------------------------------------
    OptionalKey3:            'OptionalKey3:'
--------------------------------------------------------------------------------
    \n                       '\n' (newline)
--------------------------------------------------------------------------------
    (?P<OptionalKey3>         group and capture to "OptionalKey3":
--------------------------------------------------------------------------------
      .*                       any character (0 or more times
                               (matching the most amount possible))
--------------------------------------------------------------------------------
    )                        end of "OptionalKey3"
--------------------------------------------------------------------------------
  )?                       end of grouping
--------------------------------------------------------------------------------
  \z                       the end of the string

【讨论】：

啊，诀窍是在末尾添加\z，以便强制匹配整个文本。谢谢！