It seems that you're just trying to remove all whitespaces:

s/\s+//g;
[download]

Of course that doesn't verify your data, so you could use split instead (untested):

OUTER:
while (<>){
   chomp;
   my @items = split m/\s/;
   for my $i (@items) {
       last OUTER unless $i =~ m/^[a-f\d]{2}$/;
   }
   print join '', @items;
}
[download]