How to create a frequency list of every word in a file?

Question

I have a file like this:

This is a file with many words.
Some of the words appear more than once.
Some of the words only appear one time.

I

Answer 1

#!/usr/bin/env bash

declare -A map 
words="$1"

[[ -f $1 ]] || { echo "usage: $(basename $0 wordfile)"; exit 1 ;}

while read line; do 
  for word in $line; do 
    ((map[$word]++))
  done; 
done < <(cat $words )

for key in ${!map[@]}; do 
  echo "the word $key appears ${map[$key]} times"
done|sort -nr -k5