Someone

my $section;
my %values;
while (<>) {
        if (/\[PS_(.*)\]/) {
                $section=$1;
        } elsif (/=(.*)$/) {
                $values{$section}.=',' if $values{$section};
                $values{$section}.=$1;
        }
}
my ($k) = reverse (sort (keys %values));
print "$values{$k}\n";