The following seems to work for me -- even though I left out important things like "use strict;" (I wanted to make a worst-case scenario ;^). So the trick for you is to figure out what you're doing that's different.

This is the whole program: it puts up an Entry and a Button; when you push the button, it prints whatever is in the entry at that moment. See if it does that for you.

use Tk;

$main=MainWindow->new();
$main->Entry(-width => 20,
             -textvariable => \$regex,
             )->pack();
$main->Button(-text=>"Print me",
              -command => sub{ print "$regex\n" }
              )->pack();
MainLoop;
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