'Do something' if key exists in hash1 and not in hash2 - perl

Question

I've written some code that finds overlapping keys in 3 different HoAs that contain some information on which I sort them later:
#!/usr/bin/perl
use warnings;
use strict;
my #intersect;
for my $key (sort keys %hash1) {
if (exists $hash2{$key} && $hash3{$key} ) {
my ($hit1, $percent_id1) = #{ $hash1{$key}[-1] };
my ($hit2, $percent_id2) = #{ $hash2{$key}[-1] };
my ($hit3, $percent_id3) = #{ $hash3{$key}[-1] };
push #intersect, "$key\tC1:[$condition1]$hit1 [$percent_id1]\tC2:[$condition2]$hit2 [$percent_id2]\tC3:[$condition3]$hit3 [$percent_id3]\n\n";\n";
}
}
I'm trying to adapt the script to also find keys that exist in:
hash1 and hash2, but not hash3
hash2 and hash3, but not hash1
hash1 and hash3, but not hash2
For which I'm using (e.g. for the first instance):
elsif (exists $hash2{$key} && !exists $hash3{$key} ) { # Is this the right way to specify a 'not exists'?
my ($hit1, $percent_id1) = #{ $blast1{$key}[-1] };
my ($hit2, $percent_id2) = #{ $blast2{$key}[-1] };
push #intersect, "$key\tC1:[$condition1]$hit1 [$percent_id1]\tC2:[$condition2]$hit2 [$percent_id2]\n";
}
Later in the code I loop through each #intersect in order to rank them (the details of what's going on below are largely irrelevant):
foreach (#intersect) {
chomp;
my (#condition1_match) = ($_ =~ /C1:.*?Change:(-?\d+\.\d+|-?inf)/);
#q_value1 = ($_ =~ /C1:.*?q:(\d+\.\d+)/);
my (#percent_id) = ($_ =~ /C\d+:.*\[(\d+\.\d+)\]/);
push #percentages, "#percent_id%";
my (#condition2_match) = ($_ =~ /C2:.*?Change:(-?\d+\.\d+|-?inf)/);
#q_value2 = ($_ =~ /C2:.*?q:(\d+\.\d+)/);
my (#condition3_match) = ($_ =~ /C3:.*?Change:(-?\d+\.\d+|-?inf)/);
#q_value3 = ($_ =~ /C3:.*?q:(\d+\.\d+)/);
my $condition1_match = $condition1_match[0] // $condition1_match[1];
my $condition2_match = $condition2_match[0] // $condition2_match[1];
my $condition3_match = $condition3_match[0] // $condition3_match[1];
if (abs $condition1_match > abs $condition2_match && abs $condition1_match > abs $condition3_match) {
push #largest_change, $condition1_match;
}
elsif (abs $condition2_match > abs $condition1_match && abs $condition2_match > abs $condition3_match) {
push #largest_change, $condition2_match;
}
else { push #largest_change, $condition3_match}
Obviously in the case where a key exists in two, but not three hashes, there will be a lot of instances where variables are undef, and as such I get a lot of Use of uninitialized value in...
Should I be prefixing each variable with if (defined ($variable )) ??

Answer 1

my %seen;
++$seen{$_} for keys(%hash1), keys(%hash2), keys(%hash3);
for (keys(%seen)) {
next if $seen{$_} != 2;
print("$_ is found in exactly two hashes\n");
}
This version tracks where the keys came from:
my %seen;
push #{ $seen{$_} }, 'hash1' for keys(%hash1);
push #{ $seen{$_} }, 'hash2' for keys(%hash2);
push #{ $seen{$_} }, 'hash3' for keys(%hash3);
for (keys(%seen)) {
next if #{ $seen{$_} } != 2;
print("$_ found in #{ $seen{$_} }\n");
}