regex - Regular Expressions and negating a whole character group

Question

This question already has answers here:

Answer 1

Using a character class such as [^ab] will match a single character that is not within the set of characters. (With the ^ being the negating part).

To match a string which does not contain the multi-character sequence ab, you want to use a negative lookahead:

^(?:(?!ab).)+$

And the above expression disected in regex comment mode is:

(?x)    # enable regex comment mode
^       # match start of line/string
(?:     # begin non-capturing group
  (?!   # begin negative lookahead
    ab  # literal text sequence ab
  )     # end negative lookahead
  .     # any single character
)       # end non-capturing group
+       # repeat previous match one or more times
$       # match end of line/string