preg_replace vs preg_filter

Question

What are the differences between preg_replace and preg_filter? Are there any advantages when using one of them instead of the other in certain situations? I tried reading the docs but still don't quite understand what the differences are. Please enlighten me. Thanks.

Answer 1

The advantage of preg_filter over preg_replace is that you can check whether or not anything was replaced, because preg_filter returns null if nothing was replaced, while preg_replace returns the subject regardless.

$subject = 'chips';
$pattern = '/chops/';
$replacement = 'flops';

if (is_null(preg_filter($pattern, $replacement, $subject)) { // true
    // do something
}

echo preg_replace($pattern, $replacement, $subject); // 'chips'

Answer 2

preg_filter() is identical to preg_replace() except it only returns the (possibly transformed) subjects where there was a match. For details about how this function works, read the preg_replace() documentation.

from: here

So if the signature is

preg_filter ( mixed $pattern , mixed $replacement , 
              mixed $subject [, int $limit = -1 [, int &$count ]] )

it returns the $subject arguments "transformed" (all the match with regex pattern are substitute) into an array