问题描述
我正在尝试在往后看和向前看中进行多次匹配
假设我有以下字符串：
$ Hi,this is an example @
正则表达式：(?<=$).+a.+(?=@)
我希望它在这些边界内返回两个“ a”，有没有办法只用一个正则表达式呢？
引擎：Python
解决方法
如果可以在后面使用量词，请使用
(?<=\$[^$@]*?)a(?=[^@]*@)
请参见proof。
说明
--------------------------------------------------------------------------------
(?<= look behind to see if there is:
--------------------------------------------------------------------------------
\$ '$'
--------------------------------------------------------------------------------
[^$@]*? any character except: '$' and '@' (0 or more
times (matching the least amount possible))
--------------------------------------------------------------------------------
) end of look-behind
--------------------------------------------------------------------------------
a 'a'
--------------------------------------------------------------------------------
(?= look ahead to see if there is:
--------------------------------------------------------------------------------
[^@]* any character except: '@' (0 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
@ '@'
--------------------------------------------------------------------------------
) end of look-ahead
PCRE模式：
(?:\G(?<!^)|\$)[^$]*?\Ka(?=[^@]*@)
说明
--------------------------------------------------------------------------------
(?: group,but do not capture:
--------------------------------------------------------------------------------
\G where the last m//g left off
--------------------------------------------------------------------------------
(?<! look behind to see if there is not:
--------------------------------------------------------------------------------
^ the beginning of the string
--------------------------------------------------------------------------------
) end of look-behind
--------------------------------------------------------------------------------
| OR
--------------------------------------------------------------------------------
\$ '$'
--------------------------------------------------------------------------------
) end of grouping
--------------------------------------------------------------------------------
[^$@]*? any character except: '$' and '@' (0 or more times
(matching the least amount possible))
--------------------------------------------------------------------------------
\K match reset operator
--------------------------------------------------------------------------------
a 'a'
--------------------------------------------------------------------------------
(?= look ahead to see if there is:
--------------------------------------------------------------------------------
[^@]* any character except: '@' (0 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
@ '@'
--------------------------------------------------------------------------------
) end of look-ahead