To clear up some confusion about ++: To increment by one, use, as toolic did, s++. What about ++s? That's a little different. I put a simple sample together that'll help you get a feeling for it.

#!/usr/bin/perl

use strict;
use warnings;

my(@fields) = (1, 2, 3, 4, 5, 6, 
               7, 8, 9, 10, 11, 12, 13);
print 
$fields[12]++, "\n",
++$fields[12], "\n";
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You could also use a counter that will automatically increment each field everytime it's run:

#!/usr/bin/perl

use strict;
use warnings;
use Tie::Counter;

tie my $counter => 'Tie::Counter';

my @fields = qw/1 2 3 4 5 6 7 8 9 10 11 12 13/;

foreach my $field(@fields) {
    print " $counter $field\n";
}
[download]