To demo one thing about HoH structures: Checking for the existence of a 2D hash key can result in the auto-vivivication of the first dimension. I don't think that this will matter in your application, but be aware that this can and does happen:

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

## This shows that if you test a multi-dimensional hash,
## Perl will "auto-vivify" the first dimension in the
## process of checking if the 2nd dimension exists.

my %apps;
$apps{"App1"}{Memory}    = 4;
$apps{"App1"}{Language}  = 'Perl';
$apps{"App1"}{CPU}       = '1.4';
$apps{"App1"}{Cores}     = '2';

print "No App8 Cores\n" if !exists $apps{App8}{Cores};
print Dumper \%apps;

__END__
No App8 Cores
$VAR1 = {
          'App8' => {},  <-- the exists() created this!!!
          'App1' => {
                      'Memory' => 4,
                      'Cores' => '2',
                      'Language' => 'Perl',
                      'CPU' => '1.4'
                    }
        };
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Instead of a HoH, of course another way is a HoA. This idea can more closely follow your input data format as csv files. Which is better, is debatable.

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use Data::Dump qw/pp/;

use constant { MEMORY    => 0,
               LANGUAGE  => 1,
               CPU       => 2,
               CORES     => 3,
             };


my $file1 =<<FILE1;
App1, 4     Perl
App2     8     Java
App3 ,8     Java
App4,4     PHP
App5     8     C#
FILE1

my $file2 =<<FILE2;
App1,1.5     2
App2     2.5     4
App3     2.8     4
App4     2.8     2
App5     2.8     2
FILE2

my %apps;

# There is certainly some error handling code missing
# but an obvious way to make a Hash of Array from these 2 files
# that maintains a "csv" array presentation...

open my $file, '<', \$file1 or die "$!";
while (my $line = <$file>)
{
   my ($app, @tokens) = split /[,\s]+/,$line;
   push @{$apps{$app}},@tokens
}

open $file, '<', \$file2 or die "$!";
while (my $line = <$file>)
{
   my ($app, @tokens) = split /[,\s]+/,$line;
   push @{$apps{$app}},@tokens
}
close $file;

# Op's requirement:
# Need to print name of apps that have CPU value 2, sorted by their 
# memory size e.g App1, App4 and App5  

# pp \%apps;  ### UNCOMMENT this to see the Hash of Array

# filter using grep to find the apps that use only 2 CORES

my @core2Apps = grep{$apps{$_}[CORES]==2} keys %apps;

# Now sort the results

my @sortedAppsbyMemory = sort{$apps{$a}[MEMORY] <=> $apps{$b}[MEMORY] 
+}@core2Apps;

foreach my $application (@sortedAppsbyMemory)
{
   print "$application @{$apps{$application}}\n";
}

__END__
Prints:
App4 4 PHP 2.8 2
App1 4 Perl 1.5 2
App5 8 C# 2.8 2

Note: App1 and App4 are equal in terms of CORES and MEMORY.
Their order is unpredictable without further specification or
considerations involving previous sorts. Above App4 sorts above
App1. How to force App1 to be above App4 in all situations is
an exercise left to the reader.
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