use strict;
use warnings;

my $max = 5;
my $str = '123456789012';
$str =~ s/(\S\S{$max,})/mySplit($1)/eg;
print $str;

sub mySplit {
    my $s = $_[0];
    my ($n, $i, @p, @r);

    ### Calculate number of pieces
    $n = ceil (length($s) / $max);

    ### Calculate length of pieces
    for ($i = 0; $i < length $s; $i++) {
        $p[$i % $n]++;
    }
    ### Get pieces
    for (@p) {
        $s =~ s/(.{$_})//;
        push @r, $1;
    }
    return join ' ', @r;
}

sub ceil {
    return $_[0] == int $_[0] ? $_[0] : int ($_[0] + 1);
}