$re = '/(?s)(?(?=\A).*?<script[^>]*>).*?(?:\K\/\/|<\/script>.*?(?:<script[^>]*>|\z)(*SKIP)(*FAIL))/m';
$str = 'Goal: Search using regex (in PowerShell) to find and highlight the JS comments within HTML script tags.
TEST#1:
don\'t match // dont find this comment here
don\'t match https://somesite.com
<script>
// find this comment here
//find this comment here
</script>
TEST#2:
<script>
passover //find this comment here
</script>
TEST#3:
<script>
// find this comment here
</script>
// dont find this comment here
TEST#4:
<script>
passover
// find this comment here
passover
//find this comment here
</script>
//dont find this comment here
TEST#5:
<script>
passover
https://somesite.com
dont find url
passover
</script>
TEST#6:
<script passover>
passover
// find this comment here
passover
passover
//find this comment here
</script>
TEST#7:
<ScRiPt>
passover //find this comment here with this included also!
passover this text
</sCrIpT>
//dont find this comment here
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php