<?php
$search = "/(L3.*?)OK(.*?L4)/";
$replace = "REPLACEMENT";
$subject = "'L1' => ('Vanessa', 'Prague', 'OK'), 'L2' => ('Alex', 'Paris', 'OK'), 'L3' => ('Paul', 'Paris', 'OK'), 'L4' => ('John', 'Madrid', 'OK')";
echo $str;
PD9waHAKCiRzZWFyY2ggPSAiLyhMMy4qPylPSyguKj9MNCkvIjsKJHJlcGxhY2UgPSAiUkVQTEFDRU1FTlQiOwokc3ViamVjdCA9ICInTDEnID0+ICgnVmFuZXNzYScsICdQcmFndWUnLCAnT0snKSwgJ0wyJyA9PiAoJ0FsZXgnLCAnUGFyaXMnLCAnT0snKSwgJ0wzJyA9PiAoJ1BhdWwnLCAnUGFyaXMnLCAnT0snKSwgJ0w0JyA9PiAoJ0pvaG4nLCAnTWFkcmlkJywgJ09LJykiOwokc3RyID0gcHJlZ19yZXBsYWNlKCRzZWFyY2gsICckMScuJHJlcGxhY2UuJyQyJywgJHN1YmplY3QpOwplY2hvICRzdHI7
'L1' => ('Vanessa', 'Prague', 'OK'), 'L2' => ('Alex', 'Paris', 'OK'), 'L3' => ('Paul', 'Paris', 'REPLACEMENT'), 'L4' => ('John', 'Madrid', 'OK')