This code works for me against a debian etch machine -- should be very similar to another flavor of Linux, though. (You also might consider the Net::SSH module..!):

#!/usr/bin/perl

use strict;
use warnings;

use Net::Telnet;

my $host = "somehost";
my $username = "test";
my $password = "password";

my $t = new Net::Telnet;

$t->dump_log('trace.log');  # detailed packet trace      

$t->open($host) or die "could not connect to $host: $!\n";
$t->print($username);
$t->waitfor('/ssword[:] $/');
$t->print($password);
$t->waitfor('/\$ *$/');

$t->print("cp a b");
$t->getline();   # read prompt
my $stdout = $t->getline();
print "stdout $stdout\n";

$t->print("echo \$?");
$t->getline();   # read prompt
my $exitcode = $t->getline();
print "exit $exitcode\n";

exit($exitcode);
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