php regex_replace在第一场比赛后停止

Question

I am trying to replace the first occurnce of css size(px|pt|em) with - so this:
64px 64px #123456 will become:
-64px 64px #123456

I am using the next regex:
preg_replace("/((-*\\d+(?:px|e[mx]|%)?)\\s(-*\\d+(?:px|e[mx]|%)?)){1,1}?/si", "-$1", $input_lines);

it works great when there are only 2 sets of sizes but when there are 4 like:
64px 64px 12px 12px #123456 in get the next results:
-64px 64px -12px 12px #123456 . what can I do to stop it after the first occurrence? Thanks!

Answer 1

With the 4. argument of preg_replace you can limit how much replace you would like to do:

http://php.net/preg_replace

limit

 The maximum possible replacements for each pattern in each subject string. Defaults to -1 (no limit). 

So you should use this way:

preg_replace("/((-*\d+(?:px|e[mx]|%)?)\s(-*\d+(?:px|e[mx]|%)?)){1,1}?/si",
"-$1", $input_lines, 1);