sub f {
   my ($arg1,$arg2,$arg3) = @_;
   .... uses arg1, arg2 arg3 ....
}

f();        # Works. ($arg1, $arg2 and $arg3 are undef.)
f(1,2,3,4); # Works. ('4' is ignored.)

##</code><code>##

sub f {
   my ($arg1) = @_;
   print(defined($arg1) ? $arg1 : '[undef]', "\n");
}

sub t1 { print("t1: "); f(); }
sub t2 { print("t2: "); &f;  }

t1('moo');  # t1: [undef]
t2('moo');  # t2: moo