This is a great place to use IPC::Open3. It will open STDOUT, STDIN and STDERR as file handle in you script. The only problem is if what you call performs blocking. To be safe, you should use IO::Select to see if there is data to read on the handles.

Here is something I have been playing with, it is rough, but you should get the idea from it.

example:

#!/usr/bin/perl -w
#

use strict;
use POSIX;
use IPC::Open3;
use IO qw( Select Handle );
$|++;

my $host   = "host";
my $login  = "login";
my $pword  = "password";
my $logfil = "/var/log/syslog";
my $cmd    = "telnet";
my $count  = 0;
my ($infh,$outfh,$errfh);
my $pid;
my $sel = new IO::Select;
open (OUTFILE, ">deneb.log");
   OUTFILE->autoflush(1);

eval { $pid = open3($infh,$outfh,$errfh, "$cmd $host" ) };
   die $@ if $@;

$sel->add($outfh,$errfh);

while (my @ready = $sel->can_read){
    foreach my $fh (@ready) {
        my $line;
        my $len = sysread $fh, $line, 4096;
        if (not defined $len) {
            die "Error reading from child: $!\n";
        } elsif ($len == 0){
            $sel->remove($fh);
        }else {
            if ($fh == $outfh){
                if ($count == 0){
                    print "$line\n";
                    print $infh "$login\n";
                    print $infh "$pword\n";
                    print $infh "tail $logfil";
                    $count = 1;
                }elsif ($count == 1){
                    print $infh "\n";
                    $count = 2;
                }elsif ($count == 2){
                    print OUTFILE $line;
                    sleep 1;
                    $count = 3;
                    print $infh "exit\n";
                }else {exit};
           }elsif ($fh == $errfh){
               print "From STDERR: $errfh\n";
           }else {
               print "Should never be here!!\n";
           }
       }
   }
}
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