my %HoH = (); #Something
my @IDs = ();
my ($key,$value);
while( ($key,$value) = each(%HoH) )
{ push(@IDs,$key) if  ($HoH{$key}{key1} eq "foo" && $HoH{$key}{key2} eq "bar") || $HoH{$key}{key4} < 10; }