sub double_it { $_[0] *= 2 }
my $x = 1;
print "\$x is $x\n";
double_it($x);
print "\$x is now $x\n";

##</code><code>##

$x is 1
$x is now 2

##</code><code>##

my ($url, @list) = @_;

##</code><code>##

sub links {
   my $url = shift;      # This removes the first element of @_
   map { "$url/$_" } @_; # You don't need return :)
}

##</code><code>##

sub some_func {
   # ... some stuff?
   my ($foo, $bar, $baz) = @_;
   # ... other stuff
}

##</code><code>##

sub some_func {
   my $self = shift;
   # Maybe do some checks with $self first?
   # ... some stuff?
   my ($foo, $bar, $baz) = @_;
   # ... other stuff
}