getlines from Net::Telnet works different (works/does not work). while loop opt?

[p1qb0d]

Hello.

I'm trying to work with Cisco hardware.

Simple script read the config:

#!/usr/bin/perl
 
use strict;
use warnings;
use Net::Telnet;
 
my $t;
my $host = "megahw";
my $username = "megauser";
my $passwd = "megapassword";
my @lines = ();
my $fh;
my $fn = "/var/tmp/t.log";
my $lline;
my @llines = ();
my $ownline;
my $screenlines;
 
$t = new Net::Telnet(Timeout => 10, Prompt => '/Username: $/');
$t->open($host);
$fh = $t->input_log($fn);
$t->login(Name => $username, Password => $passwd, Prompt => '/#$/');
$t->print("show running-config");
@lines = ();
$ownline = 1;
$screenlines = 25;
 
while (1){
    @llines = $t->getlines(All => 0);
    $lline = scalar @llines;
 
    if ($lline == $screenlines){
 
        while (scalar @llines){
            $lline = shift @llines;
            push @lines, $lline;
        }
 
        if ($ownline){
            $ownline = 0;
            $screenlines -= 2;
        }
 
        $t->put(' ');
        next;
    }else{
 
        while (scalar @llines){
            $lline = shift @llines;
            push @lines, $lline;
        }
 
        last;
    }
 
}
 
$t->print("exit");
$t->break;
$t->close;
 
while (scalar @lines){
    $lline = shift @lines;
    print $lline;
}
 

If I run it flat (script.pl) I get my own command only. t.log has:

 
 
User Access Verification
 
Username: megauser
Password: 
 
megahw#show running-config
 

If I run it via perl -d script.pl and type c(ontinue) immediately the t.log is the same.

If I run it via perl -d script.pl and go inside while(1) loop via n(ext) commands and then c(continue), the t.log has:

 
 
User Access Verification
 
Username: megauser
Password: 
 
megahw#show running-config
Building configuration...
 
Current configuration : 2201 bytes
!
! No configuration change since last restart
!
version 15.2
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
!
hostname megahw
!
boot-start-marker
!
There are many lines of config
!
end
 

That behaviour is very strange for me.

Any clues?