Multiple replace within text

PHP
2

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Two examples showing where you can put delimiters and modifiers (s=treat as single line U=ungreedy play around by removing it to see the results).

$str = '<!--FIND123FIND-->
<!--FINDabcFIND-->';

$pattern = '~<!--(.*)-->~sU';
$pattern2 = '<!--(.*)-->';

$replace = '<!--hello-->';

$out = preg_replace($pattern, $replace, $str);

echo $str."\n";
echo $out."\n";

preg_match_all("~$pattern2~sU", $str, $out2); 

echo'<pre>'; print_r($out2); echo '</pre>';