On a side note, your code

$sum += $_ for split ' ', "5 6 7 8\n", $K;

is broken! *

Because split will always also return the unsplitted remaining rest which of course can't be added.

  DB<20> use Data::Dump qw/dd/;


  DB<21>  $str = join " ", 10..15


  DB<22> dd ["$_",( split ' ', $str, $_)] for 0..6
[0, 10 .. 15]
[1, "10 11 12 13 14 15"]
[2, 10, "11 12 13 14 15"]
[3, 10, 11, "12 13 14 15"]
[4, 10, 11, 12, "13 14 15"]
[5, 10 .. 13, "14 15"]
[6, 10 .. 15]
[download]

and your desired count behavior for LIMIT=0 is actually mapped on LIMIT=1

If LIMIT is specified and positive, it represents the maximum number of fields into which the EXPR may be split; in other words, LIMIT is one greater than the maximum number of times EXPR may be split. Thus, the LIMIT value 1 means that EXPR may be split a maximum of zero times, producing a maximum of one field (namely, the entire value of EXPR).

In other words LIMIT may have a complicated design, but it's consistent.

see my other post Re: discussion: What should split( /PATTERN/, EXPR, 0 ) return better? (split-LIMIT = count and/or flag) for a working example.

*) tybalt89's hint was maybe a bit too subtle ;)