Hello wangruonan,

Your code has the following skeletal form:

my @headers;

for $a (@list)
{
    open(my $data, ...);

    while (my $line = <$data>)
    {
        while (my $fields = $csv->getline( $data ))
        {
            push @headers, $fields->[$a];
        }
    }

    print LOG $headers[2], "\t";
    close $data;
}
[download]

The obvious problem here is that once @headers contains at least 3 elements, the output will always be the same, viz., the third element!

But it’s also important to note that reading from the filehandle $data directly — my $line = <$data> — and via getline — my $fields = $csv->getline( $data ) — is a logic error. You shouldn’t need the outer while loop; re-write the inner one to traverse the whole file.

Hope that helps,