@arr = ('x', 'y', 'z');
# error occurs so $! is set. But thinking that this small piece of code wont cause any error I dont check for $! here.
#some more code her
print join(',', @arr);

open(FILE, "<file.txt") || die (".....error");
# check for $! here
if ($!)
{
# whcih is the culprit line causing this error? is it array allocation, or is it print or is it open?
}