## perl sub &mkssh to create an SSH session to given host using publickey-auth
# example: $ssh = mkssh("hipsxxc3");
sub mkssh {
        use IO::Pty ();
        use Net::Telnet;

        my $tmp = '';
        #chomp(my $cmd_ssh = `which ssh`); # wrong on hipsscr01 :-(
        my $cmd_ssh = "/usr/bin/ssh";
        my $host = shift;
        my $user = $ENV{USER};
        my $tmp = shift if @_;
        $user = $tmp if $tmp;
        my $port = 22;
        $tmp = shift if @_;
        $port = $1 if $tmp =~ /\d+/;
        my $cmd = "$cmd_ssh -l $user -p $port $host";
        my($pid, $pty, $tty, $tty_fd, $ssh, $telnet);

        &debug("mkssh:\thost: $host", "\tuser: $user", "\tport: $port", "\tcmd: $cmd");

        # new pseudo terminal
        $pty = new IO::Pty or die $!;

        # used for killing zombies
        $SIG{CHLD} = 'IGNORE';

        # fork process
        $pid = fork;

        unless ($pid) { # child process
                die "problem spawning program: $!\n" unless defined $pid;

                # reset SIG_CHLD, essentially for exec() call
                $SIG{CHLD} = 'DEFAULT';

                ## Disassociate process from existing controlling terminal.
                # has no effect
                #use POSIX ();
                #POSIX::setsid or die "setsid failed: $!";

                ## Associate process with a new controlling terminal.
                $tty = $pty->slave;
                $tty_fd = $tty->fileno;
                close $pty;

                ## Make stdio use the new controlling terminal.
                open STDIN, "<&$tty_fd" or die $!;
                open STDOUT, ">&$tty_fd" or die $!;
                open STDERR, ">&STDOUT" or die $!;
                #open STDERR, ">&$tty_fd" or die $!;
                close $tty;

                ## Execute requested program.
                exec $cmd or die "problem executing $cmd\n";
        }

        new Net::Telnet (       fhopen => $pty,
                                telnetmode => 0,
                                errmode => "die",
                                cmd_remove_mode => 1,
                                ors => "\r",
                                timeout => 15
                                );
}

## perl sub &debug for debugging or tracing output (if global $debug is true)
# example: &debug("message 1", $msg2, @other_msgs);
sub debug { local $\ = "\n"; local $" = "\n"; print STDERR "@_" if $debug }

## creation of SSH session with &mkssh
$tmp = &mkssh("dhcpserver");
$tmp->prompt($prompt_dhcp);
$tmp->waitfor($tmp->prompt);
$tmp->cmd(String => $nrcmd, Prompt => "/username: /");
$tmp->cmd(String => $user_nrcmd, Prompt => "/password: /");
$tmp->cmd($pass_nrcmd);

# the login works, the execution of commands, too.
# but the child process /usr/bin/ssh -l .. -p .. .. keeps existing. it's a zombie.
# and on the dhcp-server, there are zombies, too.
# how to avoid these zombies? the "use posix" and the $SIG{CHLD} lines have no effect. :(