johngg@shiraz:~/perl/Monks > perl -Mstrict -Mwarnings -E '
open my $file1FH, q{<}, \ <<__EOD1__ or die $!;
App1,4,Perl
App2,8,Java
App3,8,Java
App4,4,PHP
App5,8,C#
__EOD1__

my %apps;
while ( <$file1FH> )
{
    chomp;
    my( $key, $mem, $lang ) = split m{,};
    $apps{ $key }->{ mem }  = $mem,
    $apps{ $key }->{ lang } = $lang;
}

close $file1FH or die $!;
open my $file2FH, q{<}, \ <<__EOD2__ or die $!;
App1,1.5,2
App2,2.5,4
App3,2.8,4
App4,2.8,2
App5,2.8,2
__EOD2__

while ( <$file2FH> )
{
    chomp;
    my( $key, $cpu, $cores ) = split m{,};
    $apps{ $key }->{ cpu }   = $cpu;
    $apps{ $key }->{ cores } = $cores;
}

say for
   sort { $apps{ $a }->{ mem } <=> $apps{ $b }->{ mem } }
   grep { $apps{ $_ }->{ cores } eq q{2} }
   sort keys %apps;'
App1
App4
App5