how to run command on telnet command prompt in perl script - linux

Question

i am executing telnet command in perl script as below.
$telnetOutput = `telnet localhost 4505`;
print "\n telnet command output: $telnetOutput \n";
$clients = `clients`;
print"\n $clients\n";
$clientNumber_or_anyOtherKey = `1`;
print "\n $clientNumber_or_anyOtherKey \n";
$pollers = `pollers`;
print "\n $pollers\n";`
but after running $telnetOutput = `telnet localhost 4505`; command, as we know it will open telnet command prompt but all other commands are still executing in same old command prmopt so it's saying clients or 1 or pollers are not recognized as internal or external commands.
can any 1 help me out pls?
thanks in advanch

Answer 1

Communicating with external processes like telnet is more complicated than you might imagine, as you have to correctly handle buffering, waiting for input, and so on.
The canonical way to approach this is to use Expect ( https://metacpan.org/module/RGIERSIG/Expect-1.21/Expect.pod ) if you really need full interaction.
If you don't actually need interaction then a remote command runner like ssh or rsh (which you can call from perl of course) is sufficient.

Answer 2

this is working example for telnet connection to d-link des-1228 router and executing 2 commands. change it if you want:
#!/usr/bin/perl
use strict;
use warnings;
use Net::Telnet;
my $params;
$params{'login'}='root';
$params{'password'}='hardpass';
$params{'default_prompt'}='/DES-[^:]+:.#/'; #change it to regexp matching your prompt
my $host = '192.168.1.20';
my $t=new Net::Telnet(Timeout=>5, Prompt=>$params{'default_prompt'}, Errmode=>sub{next;});
$t->open(Host=>$host, Timeout=>2);
my $res=$t->login($params{'login'}, $params{'password'});
return if $res!=1;
$t->cmd('disable clipaging');
my #lines=$t->cmd('show fdb'); #output here
$t->close();

Answer 3

install TCL (ActiveTcl8.5.13.0.296436-win32-ix86-threaded.exe for windows) in system.
Then install Expect Package from Command from as teacup install Expect
run below script after modification for requirement
#!/usr/bin/expect -f
#!usr/bin/expect
package require Expect
# Test expect script to telnet.
spawn telnet localhost portnumber
expect "TradeAggregator>"
send "3\r"
expect "Client:"
send "1\r"
expect "1-Client>"
send "2\r"
expect "Client Pollers"
send "2\r"
expect "1-NYMEX UTBAPI"
send "1\r"
expect "2-NYMEX UTBAPI"
send "Test_123\r"
expect "Are"
send "n\r"
send "exit\r"
send "exit\r"
send "exit\r"
# end of expect script.