Just for reference: a Perl 6 version:

    sub MAIN($limit = Inf) {
        my %bag is Bag = words.map(&lc);
        say "{.key}\t{.value}" for %bag.sort( {
          $^b.value cmp $^a.value || $^a.key cmp $^b.key
        } )[^$limit]
    }

And for what it's worth, the `words` function is lazy, so it won't read all of the words into memory first.

I would have written the sort differently

    %bag.sort({ -.value, .key })

Python is relatively short, batteries included and all that:

  import re
  import sys
  import collections
  
  words = re.findall('[a-z]+', sys.stdin.read().lower())
  c = collections.Counter(words)
  for word, count in c.most_common(int(sys.argv[1])):
      print(f'{count:>7} {word}')

Three times the character count of the Unix pipe version, but IMHO a lot more readable (and generalisable).

You don't want to read all input into memory first.

Fair enough.

  import re
  import sys
  import collections
  
  c = collections.Counter()
  for line in sys.stdin:
      words = re.findall('[a-z]+', line.lower())
      c.update(words)
  for word, count in c.most_common(int(sys.argv[1])):
      print(f'{count:>7} {word}')