- preg_replace: documentation ( source)
<?php
$str = 'else if($rule==\'somerule1\')
echo \'{"s":1,"n":"name surname"}\';
else if($rule==\'somerule2\')
echo \'{"s":1,"n":"another text here"}\';';
$rule = "somerule1";
$pattern = "/else if\(\\\$rule=='$rule'\)\necho '{\"s\":\d+,\"n\":\"[^\"]*\"}';/";
$str = preg_replace($pattern, "", $str);
echo $str;