Regular expression using negative lookbehind not working in Notepad++

Question

I have a source file with literally hundreds of occurrences of strings flecha.jpg and flecha1.jpg, but I need to find occurrences of any other

Answer 1

Are you aware that you're only matching (in the sense of consuming) the extension (.jpg)? I would think you wanted to match the whole filename, no? And that's much easier to do with a lookahead:

\b(?!flecha1?\b)\w+\.jpg

The first \b anchors the match to the beginning of the name (assuming it's really a filename we're looking at). Then (?!flecha1?\b) asserts that the name is not flecha or flecha1. Once that's done, the \w+ goes ahead and consumes the name. Then \.jpg grabs the extension to finish off the match.