foo($pflicht1, $pflicht2, opt1 => 123, opt3 => 456);

sub foo {
  my $pflicht1 = shift;
  my $pflicht2 = shift;
  my %opt = ( opt1 => "Default_für_opt1",
              opt2 => "default-opt2",
              @_); 

  say $opt{opt1}; # 123
  say $opt{opt2}; # default-opt2
}