::function! Linenum()

  :if !has('perl')
    :echo "¡Lo siento, no hay Perl!"
    return
  :endif

  perl <<EOT
        $numlen = length($curbuf->Count());
        for $num (1..$curbuf->Count()) {
          $newline = sprintf "%0.*d %s", $numlen,
                             $num, $curbuf->Get($num);
          $curbuf->Set($num, $newline);
        }
EOT
:endfunction

:command! Linenum :call Linenum()