The great thing about regular expression languages is that there are so many to choose from!
Before you ask a question about regular expressions, you should make sure you and your audience agree on which regular expression language you are talking about.
You can use that table to solve this customer’s problem:
C:\> findstr /r /c:"a(?!.*b)" file.txt (prints no results!) C:\>
My goal is to find all lines that contain an
anot followed anywhere by a