my @base = stat($FILE);
my $base = "@base[0,1,10]"; # dev/ino/ctime
while (1) {
  ... read $FILE here, and process it ...
  while (1) {
    my @new = stat($FILE);
    my $new = "@new[0,1,10]"; # current dev/ino/ctime
    if ($base ne $new) { # changed
      $base = $new; # reset
      last; # restart outer loop
    }
    sleep 1; # delay because no change
  }
}