my $tgs = @_;

##</code><code>##

my ($tgs) = @_;

##</code><code>##

my $tgs = shift;

##</code><code>##

my %Test_hash;
...
sub xyz
{
    my ($tgs) = @_;
    $Test_hash{$tgs} = {a => 1, b => 2};
    ...
}
...