G'day rubystallion,

Welcome to the Monastery.

The approach I took was to read the spec, grab the DATA and write the code. I didn't spend a lot of time looking at your code initially; although, I have commented on it further down in my post. Here's what I came up with:

#!/usr/bin/env perl -l

use strict;
use warnings;
no warnings 'uninitialized';

my @key_value_pairs;

# Capture key-value pairs from original query strings
while (<DATA>) {
    chomp;
    push @key_value_pairs, { map { (split /=/)[0,1] } split /&/ };
}

# Remove common key-value pairs
KEY: for my $key (keys %{$key_value_pairs[0]}) {
    for my $i (1 .. $#key_value_pairs) {
        next KEY unless $key_value_pairs[0]{$key} eq $key_value_pairs[
+$i]{$key};
    }
    delete $key_value_pairs[$_]{$key} for 0 .. $#key_value_pairs;
}

# Recreate query strings without common key-value pairs
for my $kvp (@key_value_pairs) {
    print join '&', map { join '=', $_, $kvp->{$_} } sort keys %$kvp;
}

__DATA__
a=1&b=1&c=1&d=2&e=&f=3
a=1&b=2&c=3&d=2&e=&f=4
a=1&b=2&c=5&d=1&e=&f=5
[download]

Output:

b=1&c=1&d=2&f=3
b=2&c=3&d=2&f=4
b=2&c=5&d=1&f=5
[download]

From the comments embedded in the code, you can see three distinct steps: capture all the initial data; remove the common data; recreate the query strings with what's left.

As you indicated (i.e. "in my head it's very simple") this was fairly straightforward:

1. split on '&' and then on '='
2. only delete if all equality tests are TRUE
3. join with '=' and then with '&'

"Is there any way to make the code significantly simpler or make it easier for me to write something like this bug-free the first time?"

That's a little difficult to answer without knowing what you did on your first three attempts.

• Perhaps a lack of an initial design?
• Perhaps you had problems with poorly named variables? I certainly did! As soon as I saw your first runtime statement (my @F1;), I realised I was going to have to read more code to find out what F1 represented.
• Did you somehow get caught up with "use v5.020;"? Although I tested my code under v5.22.0, I suspect it'll run on any Perl5 released this century.

A couple of notes on command switches:

• By using the -l command switch, my print works like say (no need to add "\n").
• The -w command switch is a poor choice. The warnings pragma is better; the documentation explains why.

And, of course, if anything else in my code needs further explanation, just ask.