%foo = ( a => 1, b => 2, c => 3 };

sub mysub {
  my %x = shift;
...
}

##</code><code>##

my %foo = ( a => 1, b => 2, c => 3 );

mysub(\%foo);

sub mysub {
  my %x = %{scalar shift};

  foreach ( sort keys %x ) {
    print "$_ -> $x{$_}\n";
  }
}

##</code><code>##

my %foo = ( a => 1, b => 2, c => 3 );

mysub(\%foo);

sub mysub {
  my $x = shift;
  my %x = %{$x};

  foreach ( sort keys %x ) {
    print "$_ -> $x{$_}\n";
  }
}

##</code><code>##

my %foo = ( a => 1, b => 2, c => 3 );

mysub(\%foo);

sub mysub {
  my %x = %{shift};

  foreach ( sort keys %x ) {
    print "$_ -> $x{$_}\n";
  }
}