Sorry, there should be this:
@seen{@list} = map{($seen{$_}||0)+1} @list;

and to print the output into a file, just say:

open my $output_fh, '>', "filename.txt" or die $!;
#while(my($string, $count) = each %seen){
foreach my $string(sort {$seen{$b} <=> $seen{$a}} keys %seen){
    my $count = $seen{$string};
    printf $output_fh "%-70s%d\n", $string, $count;
}
close $output_fh;
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