my %application;  # <-- Hash!

print "Application = ", $data[$application_pos], "\n";
if ( $data[$application_pos] ne "" && $data[$ip_address_pos] ne "" ) {
    my $key = $data[$application_pos];
    push @{ $application{$key} }, $data[$ip_address_pos];  # Pushing to a HoA.
    print Dumper( \%application ) ;
}