That's so much clearer! The solution is:

my %counts;
while (<$fh>) {
   chomp;
   my @fields = split /\t/;
   $counts{ $fields[3] }++;
}
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You can print the results as follows:

for ( sort { $a <=> $b } keys %counts ) {
   print("$_: $counts{$_}\n");
}
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By the way, I said it was clearer, but it still not that clear. You still used the word "extract", for starters. It appears to mean "count" in this case. You could have said "Count how many times each different value occurs in the 4th column", but you decided to talk about how to do it (code) instead of of what you want (data).