foreach my $n (keys %emp) {
  push(@{$data{'A'}},$emp{$n}{'Emp'}) if $emp{$n}{'Org'}=~/ABC/;
  push(@{$data{'B'}},$emp{$n}{'Emp'}) if $emp{$n}{'Org'}=~/DEF/;
}

##</code><code>##

foreach(keys %data){
  open(DATA,">group$_.txt")||die"Couldn't open file for $_:$!";
  print DATA join("\n",@{$Data{$_}});
  close(DATA);
}