sub make_sub_for_given_key
{
   my( $key ) = @_; # amongst other arguments

   return sub {
      # this sub "knows" what $key is, forever.
      print "Hi! I belong to key '$key'\n";
   }
}

my $key = "Tuesday";

my %hash;
$hash{ $key } = make_sub_for_given_key( $key );

# later on, ask each sub what key it belongs to:

for $key ( keys %hash ) {
   $hash{$key}->();
}