<?php
$s = file('php://stdin');
$t = $s[0];
while ($t != $u = preg_replace(array('_/\|(?!\\\\)_', '_(?<!/)\|\\\\_', '/ /'), array('/ ', '\\\\\\', '/'), $t))
$s[] = $t = $u;
echo join("\n", $s);
?>
Note that non-ascii characters in the above source code will be escaped (such as \x9f).