英文:
Regex expression to get the string between two strings,or until either end of the main string
问题
(?<=foo|^).*?(?=bar|$) 应该可以满足你的需求，它可以匹配在String1（"foo"）和String2（"bar"）之间的内容，如果其中一个字符串不存在，也会匹配到主字符串的末尾。
英文:
I am trying to write a regex that gets the content between two strings, String1 and String2 but in case either of the two strings are not present I want to match until the end of the main string.
For example: hi_foo123xyz2-3bar_hello, foo123xyz2-3bar , foo123xyz2-3 123xyz2-3bar and 123xyz2-3 the intended match is 123xyz2-3.
I tried different approaches using Lookaheads and Lookbehinds and I feel that I only need a single step but It seems far from reach.
The closest I could get is something like this
(?<=foo).*?(?=bar|$)
I also tried
(?<=foo|^).*?(?=bar|$)
but it seems to break everything.
答案1
得分: 0
匹配的技巧是仅当没有 foo 出现时才匹配 ^，使用这个表达式 ^(?!.*foo)，然后创建一个 foo 的肯定后发断言的选择。
类似地，使用一个 bar 的前瞻断言 或者 输入的结尾 $。
(^(?!.*foo)|(?<=foo)).*?((?=bar)|$)
查看演示链接。
请注意，选择是从左到右匹配的，也就是说，只有在左边的不匹配时才尝试右边的匹配。
英文:
The trick is to match ^ only when there is no foo using this expression ^(?!.*foo), then create an alternation of that or a lookbehind for foo.
Similarly, use a lookahead for bar or end of input $.
(^(?!.*foo)|(?<=foo)).*?((?=bar)|$)
See live demo.
Recall that alternations are match left to right - ie the right is only attempted if the left doesn't match.
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