Capture a match of the key itself, which you can then use in the replcement part of the regex to get your hash key:

$text =~ s/\#(\w+)\#/$hash{$1}/g;
[download]

-----------------------------------------------------
Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
"I can see my house from here!"
It's not what you know, but knowing how to find it if you don't know that's important