for my $key (keys %hash) {
   if (exists $hash{$key}{FILE1}) {
      if (exists $hash{$key}{FILE2}) {
         # Key exists in both files
      }
      else {
         # Key exists only in file 1
      }
   }
   else {
      # Key exists only in file 2
   }
}

##</code><code>##

foreach my $key (keys (%hasha)) {
   if (my @temp = grep( /$key/, @prevarray ) ) {
      push(@{$hasha{$key}},$value);
      next;
   }
   else {
      push (@{$hashb{$key}},$value);
      next;
   }
}

##</code><code>##

foreach my $key (keys (%hasha))
   {
   if (my @temp = grep( /$key/, @prevarray ) )
      {
      push(@{$hasha{$key}},$value);
      next;
      }
   else
      {
      push (@{$hashb{$key}},$value);
      next;
      }
   }

##</code><code>##

foreach my $key (keys (%hasha))
{
   if (my @temp = grep( /$key/, @prevarray ) )
   {
      push(@{$hasha{$key}},$value);
      next;
   }
   else
   {
      push (@{$hashb{$key}},$value);
      next;
   }
}