I'm trying to write a simple program to communicate with the serial port. I am able to send commands, but getting what is sent back has proven difficult. I cannot use Win32::SerialPort, or Device::SerialPort.

I had limited success with:

my $COM_PORT = "com1";
open DEV,"+<", "$COM_PORT" or die "failed to open com port\n";
print DEV "\n";
$input = <DEV>;
[download]

But it can hang on $input = <DEV> when there is no incoming data.

I have played around with sysopen and IO::Select, but I can't get any of the select functions to recognize the Serial port as ready to read/write.

use IO::Select;
use IO::Handle;

$COM_PORT = "COM1";
my $Serial;

#system("mode com1 baud=9600 stop=1 data=8 parity=n rts=on dtr=on");
#open $Serial,"+<", "$COM_PORT" or die "failed to open com port\n";
sysopen $Serial,"$COM_PORT", O_RDWR|O_NDELAY|O_NCOTTY or die "failed t
+o open com port\n";
my $fd = fileno($Serial);
close ($Serial);

print "File Descriptor is: $fd \n";

$sel = IO::Select->new;
$sel -> add($Serial);

if($sel -> exists($Serial))
{
    print "Handle exists \n";
}

print $Serial "\n";

my $timeout = 0;

if (my @ready = $sel -> can_read(0))
{
    print "Ready to read! \n";
}

if (my @ready = $sel -> can_write(0))
{
    print "Ready to write! \n";
}

if(my @ready = $sel -> has_error(0))
{
    print "Exceptions found! \n";
}

close ($Serial);

print "Finished... \n";
[download]

But when run, this simply outputs:
Handle Exists
Finished...

What am I doing wrong? Does anyone know how to simply check if there is any incoming data on the serial port without Win32::SerialPort?

Thanks!

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