Got it, let's sort out this regex issue for you. The problem with your current pattern (?<!@if\(null\)).*?@end$ is that the negative lookbehind only checks if the immediate left of the current position isn't @if(null)—but when your string starts with @if(null), the regex still matches the whole thing because the lookbehind doesn't account for the start of the string properly.

The Correct Regex for Your Exact Need #

If you only want to extract content specifically when the condition is @if(Medellin), use this pattern:

^@if\(Medellin\)\s*(.*?)\s*@end$

Let's break down what this does:

• ^ anchors the match to the start of the string, so we only match strings that begin with our target condition.
• @if\(Medellin\) exactly matches the opening condition (we escape parentheses with \ because they're special regex characters).
• \s* matches any optional whitespace between the condition and your content.
• (.*?) is a non-greedy capture group that grabs your desired content (in this case, "City Medellin").
• \s*@end$ matches optional whitespace followed by the closing @end, anchored to the end of the string.

How It Works With Your Test Strings #

1. For @if(Medellin) City Medellin @end:
   • The regex matches the entire string, and the capture group returns City Medellin (exactly what you want).
2. For @if(null) City Medellin @end:
   • The regex doesn't match at all because the start of the string doesn't match @if(Medellin)—so no content is extracted, which is correct.

A More Flexible Version (If You Need It) #

If you ever want to extract content for any @if(...) condition except @if(null), you can use this pattern instead:

^@if\((?!null\))[^)]+\)\s*(.*?)\s*@end$

Here, (?!null\)) is a negative lookahead that ensures the content inside @if() isn't "null", and [^)]+ matches any valid condition text.

That should solve your problem perfectly!

内容的提问来源于stack exchange，提问作者Vladislav