Detecting Linux boot with perl and serial device

Question

I am writing a perl script that boots a linux image and needs to detect if the image reached the login prompt. i am using the Device::serial module to communicate with the development board. i am running into problems detecting the login string. i think it might be related to the large amount of prints that occur during a linux boot. the code below tries to capture the prompt. strange enought it only works when i add the unnecessaty "read" command

# Wait for login prompt
$port->are_match("login:");
$gotit   = "";
$timeout = 60;
until (($gotit ne "") or ($timeout eq 0)) 
{
    $gotit = $port->lookfor;       # poll until data ready
    die "Aborted without match\n" unless (defined $gotit);
    $read = $port->read(1000000);
    $port->lookclear;
    sleep(1);
    $timeout--;
}

is "lookfor" good for the linux boot scenario at all? why does the "read" make this code work ?

thanks everyone

Answer 1

The CPAN doc page says to do this:

  my $gotit = "";
  until ("" ne $gotit) {
      $gotit = $PortObj->lookfor;       # poll until data ready
      die "Aborted without match\n" unless (defined $gotit);
      sleep 1;                          # polling sample time
  }

There is no call to $port->lookClear in their loop. I suspect this is contributing to your issue. Also be careful with that timeout.