How to delete all lines containing more than a certain number of letters?

Question

How can I delete all of the lines in a file which contain more than a given number of letters? E.g.

bear
rabbit
tree
elephant

If I restrict it to words of 5 letters or less, the output would be:

bear
tree

• The file contains various foreign characters, each of these should count as one letter.
• Punctuation symbols also can count as one letter.

Answer 1

$ awk 'length<=5' input.txt
bear
tree