DB<158> @head1= @{$arr1->[0]}
 => ("name", "pos", "loc", "age")

  DB<159> @head2= @{$arr2->[0]}
 => ("car", "dog", "age")

  DB<161> %pos=();$p=0

  DB<162> for ( @head1 , @head2 )  {
           $pos{$_}=$p++ unless exists $pos{$_}
          }

  DB<163> %pos
 => ("dog", 5, "loc", 2, "car", 4, "name", 0, "pos", 1, "age", 3)