Assuming you already have your communication link established, just send the appropriate string to that link. perlrebackslash shows that you can send a hex byte thru the "\x##" sequence, so STX would be "\x02", and thus <STX>H<EOT> would be "\x02H\x04".

Somehow it's working:


#!/usr/bin/perl

use IO::Socket;
use strict;

my( $socket,$ret );
my $maxlen  = 1024;
my $timeout = 5;
# my $data = "\x02H\x04";  # getVersion <STX>CMD<EOT>
my $data = "\x02LS9F\x04"; # getSerial <STX>CMD<CHECKSUM><EOT> 
$socket = IO::Socket::INET->new (
   PeerAddr  => '192.168.1.16',
   PeerPort  => 10001,
   Proto     => 'tcp'
) or die "ERROR in + Socket Creation : $!\n";
main::printdata('Client sends',$data );
$socket->send($data) or die "send: $!";
$socket->recv( $ret,$maxlen );
main::printdata('Server responded',$ret );
$socket->close();
[download]

Result:
Client sends \x02LS9F\x04
Server responded \x0200000000030000000000C3\x04

But when I add $socket->recv( $ret,$maxlen ) or die "Fail: $!"; the cmd always fails. with an empty error:
Client sends \x02LS9F\x04
Fail:

How do I increase the verbosity level to find out what's going wrong here?

How do I increase the verbosity level to find out what's going wrong here?

Item 1 in the Basic debugging checklist suggests to use warnings which you are not doing here. Enable that for starters.

$socket->recv( $ret,$maxlen ) or die "Fail: $!";

The docs for recv say:

Returns the address of the sender if SOCKET's protocol supports this; returns an empty string otherwise. If there's an error, returns the undefined value.

But your statement only tests for truth rather than definedness. Try this instead, perhaps:

$socket->recv( $ret,$maxlen ) // die "Fail: $!";

use strict;
use warnings;
use charnames ':full';

my $command = "\N{STX}H\N{EOT}";
my $reply   = "\N{STX}XTM20\N{EOT}";
[download]