use IPC::Open2;

my $pid = open2(my $chld_out, my $chld_in, 'gpg', -'u', @weitere_argumente) or die $!;
print $chld_in $message_body or die;
close $chld_in or die;
my $output = {local $/; <$chld_out>};
waitpid ($pid, 0) or die $!;