You'll need to encode the "." period for that to work correctly!!! (I couldn't help but golf it down a little, sorry.)

## No Period in the char class!
$STRING =~ s/([^a-zA-Z0-9_-])/lc sprintf(".%02x", ord($1))/eg;

## my encode
$S =~ s/([^\w-])/sprintf".%02x",ord$1/eg;
## my decode
$S =~ s/\.(..)/chr hex $1/eg;
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