#Passing scalar ref
sub make_session {
    my ($u,$a,$s)=@_;
    my $session_hash={
        user=>$u,
        dept=>$a
    };
    $$s=$session_hash;
}
&make_session($user,$dept,\$sid);

##</code><code>##

#Returning hash ref
sub make_session {
    my ($u,$a)=@_;
    $session_hash={
        user=>$u,
        dept=>$a
    };
    return $session_hash;
}
$sid = &make_session($user,$dept);