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 1

/abc(?!$)/

(?!$) is a negative lookahead. It will look for any match of abc that is not directly followed by a $ (end of line)

Tested against

• abcddee (match)
• dddeeeabc (no match)
• adfassdfabcs (match)
• fabcddee (match)

applying it to your case:

ruby-1.9.2-p290 :007 > "aslkdjfabcalskdfjaabcaabc".gsub(/abc(?!$)/, 'xyz')
  => "aslkdjfxyzalskdfjaxyzaabc"