Regex to match only the first line?

Question

Is it possible to make a regex match only the first line of a text? So if I have the text:

This is the first line.
This is the second line. ...

It would matc

Answer 1

There is also negative lookbehind function (PowerGREP or Perl flavor). It works perfectly for my purposes. Regex:

(?

where

• (? is negative lookbehind - regex matches only strings that are not preceded by a whitespace(s) (\s also stands for a line break)
• ^ is start of a string
• (.+) is a string
• $ is end of string