my %ids;
while (my $line = <PIDS>) {
    chomp $line;
    my (undef, $id) = split /\|/, $line;
    $ids{$id} = 1;
}

while (my $line = <FIDS>) {
    my ($id, $rest) = split /;/, $line, 2;
    if ($ids{$id}) {
        print "Found id '$id' in line $line";
    }
}