G'day Serene Hacker,

It would have helped if you'd shown a sample of your actual input file. The two hashrefs you show give no indication of the data source or how the data shown was extracted; in fact, I'm not at all convinced that those hashrefs are necessary, even as temporary data structures.

Purely for demonstration purposes, let's assume your input file records are URLs; and the query string (which could be empty or even absent) represents the "containing key,value pairs".

$ cat pm_11139481_csv_kv_pairs_data.txt
http://example.com/?AB1=101&NN=201&XYZ=401
http://example.net/?AB1=102&XYZ=402&MM=302
http://example.org/?MM=303&XYZ=403&NN=203&AB1=103
http://example.mil/?
https://example.mil/
http://example.edu/?PQR=504
[download]

Note that I used unique values throughout. The last digit of each matches the record number. This facilitates quickly checking the output by visual inspection. (Note: in your example, two instances of 100, and two of 400, do not allow this.)

Now, process that data with:

#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

use Text::CSV;

my $source_data = 'pm_11139481_csv_kv_pairs_data.txt';
my $created_csv = 'pm_11139481_csv_kv_pairs_data.csv';

my %data;
my $last_index = -1;
extract_data($source_data, \%data, \$last_index);

{
    my @headers = sort keys %data;
    my $csv = Text::CSV::->new();
    open my $csv_fh, '>', $created_csv;
    $csv->say($csv_fh, \@headers);

    for my $i (0 .. $last_index) {
        $csv->say($csv_fh, [map $data{$_}[$i], @headers]);
    }
}

sub extract_data {
    my ($in_file, $data, $last_index) = @_;

    open my $fh, '<', $in_file;

    while (<$fh>) {
        ++$$last_index;
        chomp;
        my $qs = (split /[?]/)[1];
        next unless defined $qs;

        for my $kv_pair (split /[&]/, $qs) {
            my ($key, $val) = split /[=]/, $kv_pair;
            $data->{$key}[$$last_index] = $val;
        }
    }

    return;
}
[download]

Obviously, you'd need to write your own version of extract_data(); however, the rest of the code should probably work pretty much as is.

Here's the result:

$ cat pm_11139481_csv_kv_pairs_data.csv
AB1,MM,NN,PQR,XYZ
101,,201,,401
102,302,,,402
103,303,203,,403
,,,,
,,,,
,,,504,
[download]