Simply put: you're printing $UIDholder in a single-quoted string, which does not expand variables. Also, you're using the word "reference" wrong. Don't use it like that. Bad mojo.
Jeff japhy Pinyan,
P.L., P.M., P.O.D, X.S.:
Perl,
regex,
and perlhacker How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart