Regular expressions: find string without substring

Question

I have a big text:

\"Big piece of text. This sentence includes \'regexp\' word. And this
sentence doesn\'t include that word\"

I need to fi

Answer 1

With an ignore case option, the following should work:

\bthis\b(?:(?!\bregexp\b).)*?\bword\b

Example: http://www.rubular.com/r/g6tYcOy8IT

Explanation:

\bthis\b           # match the word 'this', \b is for word boundaries
(?:                # start group, repeated zero or more times, as few as possible
   (?!\bregexp\b)    # fail if 'regexp' can be matched (negative lookahead)
   .                 # match any single character
)*?                # end group
\bword\b           # match 'word'

The \b surrounding each word makes sure that you aren't matching on substrings, like matching the 'this' in 'thistle', or the 'word' in 'wordy'.

This works by checking at each character between your start word and your end word to make sure that the excluded word doesn't occur.