regex - 仅当 Negative Lookahead 和 Lookbehind 都失败时匹配

Question

我正在尝试创建一个正则表达式，当且仅当它没有用单引号括起来时，它才会检查一个单词是否存在于一个句子中。

我尝试过不同的正则表达式，例如:

(?<!' )(?i:THEN)|(?i:THEN)(?! ')

匹配'然后' | ' then'，不应该匹配。

(?<!' )(?i:THEN)(?! ') or (?<!(' ))(?i:THEN)|(?i:THEN)(?!( '))

匹配不应该匹配的“then”

我真的很困惑，因为我不知道哪个 Regex 有效。我也试过其他正则表达式，但它不匹配:

' then I jumped.
He said then 'Wow'.

一些意见将不胜感激!

谢谢!

Answer 1

描述

此正则表达式将匹配单词 then没有被引号包围。

\bTHEN\b(?<!'\s*THEN(?=\s*'))

某些语言不允许交替，例如 \s?或 \s*内部回顾。因此，如果您正在使用其中一种语言，那么您需要更清楚地测试空格。

\bTHEN\b(?<!'\sTHEN(?=\s'))(?<!'THEN(?='))

例子

现场演示

https://regex101.com/r/gS4zU8/1

then             matched
'then            matched
then'            matched
'then'
' then           matched
then '           matched
' then '
' then I jumped.       matched
He said then 'Wow'.    matched
SthenS

解释

NODE                     EXPLANATION
----------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
----------------------------------------------------------------------
  THEN                     'THEN'
----------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
----------------------------------------------------------------------
  (?<!                     look behind to see if there is not:
----------------------------------------------------------------------
    '                        '\''
----------------------------------------------------------------------
    \s                       whitespace (\n, \r, \t, \f, and " ")
----------------------------------------------------------------------
    THEN                     'THEN'
----------------------------------------------------------------------
    (?=                      look ahead to see if there is:
----------------------------------------------------------------------
      \s                       whitespace (\n, \r, \t, \f, and " ")
----------------------------------------------------------------------
      '                        '\''
----------------------------------------------------------------------
    )                        end of look-ahead
----------------------------------------------------------------------
  )                        end of look-behind
----------------------------------------------------------------------
  (?<!                     look behind to see if there is not:
----------------------------------------------------------------------
    'THEN                    '\'THEN'
----------------------------------------------------------------------
    (?=                      look ahead to see if there is:
----------------------------------------------------------------------
      '                        '\''
----------------------------------------------------------------------
    )                        end of look-ahead
----------------------------------------------------------------------
  )                        end of look-behind
----------------------------------------------------------------------