regex - notepad++ - search for a string containing a string and not containing another string

Question

I am not able to solve this: I have text file with some entries like "user = ABname". I would like to search for all the lines containing user id not beginning with "AB" or "ab" and I need to do it with a regular exp using the search functionality of Notepad++. I have tried using

user = ^[ab]

but actually is not working as expected.

I should find all these:

user = CDname1
user = cdname2
user = acname3
user = xbname4

but not

user = abname1
user = ABname2

Answer 1

Try using negative look ahead:

user = (?![aA][bB]).*

You are misunderstand how a character class works. The character class - [ab] matches only one character, out of all present inside [ and ]. So, it will match either a or b. I won't match ab in sequence. Basically
[ab] is same as a|b.

Answer 2

You need to use a negative lookahead, such as:

^user = (?![Aa][Bb])