my $regex=qr/^Device(\s)+Configuration/;
...
my $result = $functions{$regex}->($var2);

##</code><code>##

my $result = undef;
for (keys %functions) {
  if (this_is_the_key_I_want($_)) {
    $result = $functions{$_}->($var2);
    last;
  }
}