Net::Telnet needs line of code added for fhopen to work with cygwin-perl and IO::Pty module in MSWin

Thu Mar 14 12:03:00 GMT 2002

Brian.Kelly@empireblue.com wrote:
> First I'd like to say THANKS!!!!

Brian, you're most welcome.
> Recently, the IO:Pty module was successfully ported to
> work with cygwin-perl. Now it is truly possible to use your
> fhopen method (per Lincoln Stein's chapter on your Telnet
> module) to do Expect-like control of interactive programs using
> your Telnet module on MSWin OS's.

I haven't seen Lincoln's book. Is that chapter available online?
> There's just one sligggghhht problem ...........
>> It seems that on a MSWin OS there is no way to truly escape the infamous
> CR\LF.
>> In your "print" subroutine, you "attempt" to do this with the following
> line of code:

The TELNET protocol specifies CR LF as an end-of-line. The
Net::Telnet::print() code you mention converts the OS native EOL
to the TELNET EOL.
If you're using Net::Telnet with a pseudo terminal then yes you
do want the EOL to be just CR.
Probably the best way to do this is just:
 $telnet->output_record_separator("\r");
Modifying Net::Telnet to convert CR LF to just CR is definitely
not the right way to do this.
Here's some code that changes a password on SunOS 5.8. Give it a
try on cygwin.
#!/usr/bin/perl
my $oldpw = "";
my $newpw = "";
use Net::Telnet;
$pwd = new Net::Telnet (Timeout => 2,
 Errmode => "return",
 Dump_log => "/tmp/dump.log");
## Start passwd program.
&spawn($pwd, "passwd")
 or die $pwd->errmsg;
## Send existing passwd.
$pwd->waitfor('/password: ?$/i')
 or die "no old password prompt: ", $pwd->lastline;
$pwd->print($oldpw);
## Send new passwd.
$pwd->waitfor('/new password: ?$/i')
 or die "bad old password: ", $pwd->lastline;
$pwd->print($newpw);
## Send new passwd verification.
$pwd->waitfor('/new password: ?$/i')
 or die "bad new password: ", $pwd->lastline;
$pwd->print($newpw);
## Display success or failure.
$pwd->waitfor('/changed/')
 or die "bad new password: ", $pwd->lastline;
print $pwd->lastline;
$pwd->close;
exit;
sub spawn {
 my($spawn) = shift @_;
 my($pty,
 $tty,
 $tty_fd);
 use IO::Pty ();
 use POSIX ();
 $pty = new IO::Pty
 or die $!;
 unless ($pid = fork) { # child process
 die "problem spawning program: $!\n" unless defined $pid;
 use POSIX ();
 POSIX::setsid
 or die "setsid failed: $!";
 $tty = $pty->slave;
 $tty_fd = $tty->fileno;

 open STDIN, "<&$tty_fd" or die $!;
 open STDOUT, ">&$tty_fd" or die $!;
 open STDERR, ">&STDOUT" or die $!;
 close $pty;
 close $tty;
 exec @_ == 1 ? $_[0] : @_
 or die "problem executing $_[0]: $!\n";
 }
 $spawn->fhopen($pty)
 or return;
 $spawn->telnetmode(0);
 $spawn->binmode(1);
 $spawn->output_record_separator("\r");
 $spawn->cmd_remove_mode(1);
 1;
} # end sub spawn
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