sub prototyped($_;$)
{
  # Here $_[0] is a compulsory argument
  # $_[1] defaults to $_
  # $_[2] may not even exist
}

sub unprototyped
{
  push @_, $_ if @_ < 2;
  # Here $_[0] is a compulsory argument
  # $_[1] defaults to $_
  # $_[2] may not even exist
}

##</code><code>##

sub unprototyped
{
  goto &unprototyped @_, $_ unless @_ > 1;
  # See comments in previous exemples
}

##</code><code>##

sub unprototyped
{
  push @_, $_ if @_ < 2;
  # Do all the work
  $_ = $_[-1];
  # Return value here
}

##</code><code>##

use v5.14;

sub f2
{
  while (<DATA>) { chomp; last; };
}
sub f1(_) 
{
  f2;
  say shift;
}

f1 "Hello ";
$_ = "World";
f1;
f1 for "!";
__DATA__
Everyone
Perlmonks