my ($in, $out, $err);
for($in,$out,$err) { $_ = \my $x }

# starting the application
my $handle = start \@args, $in, $out, $err;

# wait until prompted for input
pump $handle until $$out =~ /Login:/;        # note the dereferencing - $$out
$in .= "Boris\n";

# wait until prompted for password
pump $handle until $$out =~ /Password:/;

# and so on ...

# store them
$client_descr->{"Handle"} = $handle;
$client_descr->{"In"}     = $in;
$client_descr->{"Out"}    = $out;
$client_descr->{"Err"}    = $err;