RegEx Replace button doesn't work as expected with a look-behind.

Joe Furlong

Today I found that when using the “Replace” button when using a positive lookahead and a capture group Notepad++ doesn’t replace anything. It only iterates through like “Find Next”.

For example in the Changelog for the latest version If I wanted to remove the new lines between all the plugin versions with a regex.
Excerpt from Changelog to remove newline characters:
"

NppExport v0.2.8
Plugin Manager 1.3.5
Converter 3.0
Mime Tool 1.9
"
use the regex: (?<=.\d)(\r\n)
Set the replace with as a space or comma.

If I press “Replace All” the replace works on all 4 lines as expected. But, if I just try the “Replace” no replacements are made.
If I don’t use a lookahead the “Replace” button works as expected.

Is there a reason for this behavior?

guy038

Hello Joe,

The behaviour of the N++ regex engine is quite bugged, if your regex contains “backward” assertions, as \A or look-behind, as (?<=xxx) and also if you use the \K syntax . In that case, the step by step replacement, with the Replace button, will NEVER work :-(( Therefore, you must use the Replace All button, exclusively !

Just note that “forward” assertions, as \z and positive or negative look-ahead, as (?=xxxx) or (?!xxxx), work fine and that the use of the Replace button is effective !

BTW, many thanks to you for your regex, as a reply to greg marshall. Refer to the address, below :

https://notepad-plus-plus.org/community/topic/12362/duplicate-rows-according-to-whats-in-a-column/4

Indeed, it helped me to find out a general regex, to get all the work done, in one go !

Best Regards,

guy038

Scott Sumner

Reading this posting, it strikes me that perhaps the title should be

“RegEx Replace button doesn’t work as expected with a look-behind.”

rather than

“RegEx Replace button doesn’t work as expected with a positive lookahead.”

Joe Furlong

Scott,
You are correct on the title of the post. I posted too late, and did mean the look-behind as you mentioned. When i tried to edit the post, I was given an error stating it can only be edited withing 180 seconds. I’ll poke around a bit, and see if I have any luck to correct the title.

Guy038 thanks for the response. I did notice that other regex did appear to work. Was curious why the look behind didn’t work.

Thanks again.

Joe–

dail

Title updated.