$#data ++

##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;

my @data;
while (my $line = <>) {
    if ($line =~ /^(.*) (\d+)$/) {
        push @data, $1;
    }
}

for my $d (@data) {
        print "$d\n";
}

##</code><code>##

Modification of non-creatable array value attempted, subscript -1

##</code><code>##

my @data;
$data[-1] = 2;