As for your second question: After your sleep, you only update $pid after printing the message. Maybe consider always updating $pid directly after the sleep instead of updating it after printing in two parts of your program:

$pid = `pgrep -f '[a]bc'`;
...
until ($i > 60) {
    if ($pid) {
       $timestamp = localtime(time);
         print $fh ("$pid , $timestamp , $msg\n");
     }else{
       $timestamp = localtime(time);
        print $fh ("No pid , $timestamp\n"); 
     }
$i = $i +1;
sleep 10;
       $pid = `pgrep -f '[a]bc'`;
 }
[download]