open(FILE, '>', 'temp.txt')
   or die("Can't create output file: $!");

greet(*FILE);

sub greet {
   my ($fh) = @_;
   print $fh "Hello World\n";
}

##</code><code>##

sub foo { print("Hello World\n"); }

*bar = \&foo;

bar();

##</code><code>##

open(my $file, '>', 'temp.txt')
   or die("Can't create output file: $!");

greet($file);

sub greet {
   my ($fh) = @_;
   print $fh "Hello World\n";
}