this works for me on my CISCO's... may be it's the lines...

$telnet->prompt('/\w+# $/');
$telnet->waitfor($telnet->prompt);
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that make it work... Don't know, just figuring this out myself...
usage: ./program.pl 10.10.10.77 z.out

#!/usr/bin/perl
use strict;
use warnings;
use Net::Telnet;

my $uri = shift @ARGV or die "IP address needed \n Usage: ./runssh 10.
+10.10.77 outputfile";
my $a = shift @ARGV or die "output file needed \n usage: ./runssh 10.1
+0.10.77 outputfile";

my $telnet = new Net::Telnet  (Timeout=>15
        #,Input_log => "received_data.txt"
        ,Input_log => $a
);


$telnet->open($uri);
$telnet->waitfor('/login: /i');
$telnet->print('Place_the_login_here');
$telnet->waitfor('/Password: /i');
$telnet->print('Place_the password_here');
print "Login is successful \n";
$telnet->prompt('/\w+# $/');
$telnet->waitfor($telnet->prompt);
$telnet->cmd("terminal length 0");
$telnet->cmd("show interface brief");

$telnet->cmd("sh int desc");
$telnet->cmd("sh flogi data");
$telnet->cmd("sh zone act");
$telnet->waitfor($telnet->prompt);

my $out = $telnet->print('exit');
print $out;

$telnet->close();

my $fname = "received_data.txt";

open (my $fh, "<", $fname) or die "Can't open";
while (<$fh>) {
        print if /ip prefix-list/;
        }
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