This provides a unique value for each data item. It combines a row ID ($.) and a field ID ($i).

# data_read

use strict;
use warnings;

while (<DATA>)
{
    chomp;
    my @data = split;
    for (my $i = 0; $i <= $#data; ++$i)
    {
        print "$._$i = $data[$i]\n";
    }
}

__DATA__
qwerty qwerty qwerty asdf zxcv 1234 
qwerty qwerty qwerty asdf zxcv
[download]

Here's the output:

[ ~/tmp ] $ perl data_read
1_0 = qwerty
1_1 = qwerty
1_2 = qwerty
1_3 = asdf
1_4 = zxcv
1_5 = 1234
2_0 = qwerty
2_1 = qwerty
2_2 = qwerty
2_3 = asdf
2_4 = zxcv
[ ~/tmp ] $
[download]

Here's a perl.com article which describes $. and other special variables.