The following fix for the code provided by ccn.

Should be
($cnt = 1), push @result, '-' if $cnt > 3; not
($cnt = 0), push @result, '-' if $cnt > 3;
If $cnt = 0 then the 2nd, 3rd... group of characters in each word will be (N+1) long. In the following example the first group will be 3 characters long and all the rest groups will be 4 characters long

sub splitlong {
    my $text = shift;
    my @result;
    my ($cnt, $inside) = (0, 0);
    for (split //, $text) {
        ($inside = 0), next if $inside and $_ eq ']';
        $inside = 1 if !$inside and $_ eq '[';
        next if $inside;
        $cnt = /\s/s ? 0 : $cnt + 1;
        ($cnt = 1), push @result, '-' if $cnt > 3;
    }
    continue {
        push @result, $_;
    }
    warn "invalid input: $text" if $inside;
    return join '', @result;
}

my $text = 'ju[color=1]s[/color]t a sam[color=2]p[/color]le';

print splitlong($text);
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