http://qs321.pair.com?node_id=1091785


in reply to regex question: How do I modify in place in only one character class?

Putting aside the very odd goal...

The following regex will work for you.

By using a look behind assertion \K and a look ahead assertion, we can simply inject " selected" into the appropriate option:
$selection =~ s/<option [^>]*\K(?=>\s*\Q$value\E\b)/ selected/;