A regex that may contain a palticular pattern but not another pattern

Question

Consider the below lines:

1. यदि रेनेसाँ मिथ्या है तो इतिहास क्या है? जब हम इसके स्वाभाविक तत्वों को देखें <FIL\>

2. यदि रेनेसाँ मिथ्या है तो इतिहास क्या है? जब हम इसके स्वाभाविक तत्वों को देखें LIF

3. यदि रेनेसाँ मिथ्या है तो इतिहास क्या है? जब हम इसके स्वाभाविक तत्वों को देखें

I want to write a regex that removes lines which a) do not contain Devanagari characters b) except some exact tags ( like, <FIL\> ). So basically, it should not match line 1. and 3. but only line 2.

I tried merging a capturing group inside a negated set [^ँ-ॿ(FIL)] but apparently that doesn't work. I tried other combinations of such kind but couldn't reach the solution.

Answer 1

In C# you can use this regex:

^(?!.*?<FIL\\>)(?=.*?[^\p{IsDevanagari}\p{P}\s]).+$

RegEx Demo