Howdy AllPaoTeam, welcome to the Monastery! Athanasius already pointed out that /s+/ in your code should really be /\s+/ if you intend to split on whitespace. (That's all whitespace, BTW, not just tab characters!) And as he furthermore said, a bit of sample data that shows the problem would be good: it doesn't have to be your entire file, just a portion of it that should be handled correctly but isn't.

You can also use Text::CSV to parse such files by setting the separator to a tab character, like this:

#!/usr/bin/perl

use strict;
use warnings;
use feature qw/say/;
use Text::CSV;

my $csv = Text::CSV->new({
    sep_char    => "\t",
    binary      => 1,   # always a good idea
});

while(my $row = $csv->getline(*DATA)) {
    say "$row->[0],$row->[1]";
}

__DATA__
word1   word2   word3
word4   word5   word6
[download]

This is going to be only useful if your words are separated by precisely one tab character, though, since otherwise you'll get empty fields in between words.