php regex_replace stop after first match

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!

Might I ask why you're modifying a CSS string with JavaScript? This sounds like a very strange use-case. — Halcyon
– Halcyon, Commented Nov 26, 2013 at 13:20
@ArunKillu : this not working and as far as I know there is no g in preg_replaec @FritsvanCampen : I am parsing css files — user2979757
– user2979757, Commented Nov 26, 2013 at 13:21
don't do that y you want to parse css when browser itself parse for you — Arun Killu
– Arun Killu, Commented Nov 26, 2013 at 13:23
Otherwise if this regexp encounters with a -64px it will modify it to - - 64px... — Lajos Veres
– Lajos Veres, Commented Nov 26, 2013 at 13:25

Lajos Veres · Accepted Answer · 2013-11-26 13:21:27Z

3

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);

answered Nov 26, 2013 at 13:21

Lajos Veres

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2 Comments

user2979757 Over a year ago

Thanks, I had forgotten about this argument :-)

Álvaro González Over a year ago

Oops... I've misread a question again. I've just removed my bogus comment.

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