perl -pi.bak -e '$count++;s/^/$count. /' file_name

##</code><code>##

foreach my $line (@file) {
  (undef) = <FILE>; # stores number of lines into $.
  $count++;
  print FILE, "$count. ";
  if ($count == $.) {last; }
}

##</code><code>##

foreach my $line (@file) {
    $count++;
    print FILE, "$count. $line";
}
##</code><code>##

foreach (@file) {
    $count++;
    s/^/$count. /;
    print FILE;
}

##</code><code>##

(undef) = <FILE>; # stores number of lines into $.

##</code><code>##

if ($count == $.) {last; }