Question
The regex /abc$/ will match an abc that does appear at the end of the
line. How do I do the inverse?
I want to match abc that isn't at the end of a line.
Furthermore, I'm going to be using the regex to replace strings, so I want to
capture only abc, not anything after the string, so /abc.+$/ doesn't work,
because it would replace not only abc but anything after abc too.
What is the correct regex to use?
Answer
/abc(?!$)/
(?!$) is a [negative lookahead](http://www.regular-
expressions.info/lookaround.html). It will look for any match of abc that is
not directly followed by a $ (end of line)
Tested against
- abc ddee (match)
- dddeee abc (no match)
- adfassdf abc s (match)
- f abc ddee (match)
applying it to your case:
ruby-1.9.2-p290 :007 > "aslkdjfabcalskdfjaabcaabc".gsub(/abc(?!$)/, 'xyz')
=> "aslkdjfxyzalskdfjaxyzaabc"
