Write a bash script to calculate the frequency of each word in a text file `words.txt`.

For simplicity sake, you may assume:

- `words.txt` contains only lowercase characters and space `' '` characters.
- Each word must consist of lowercase characters only.
- Words are separated by one or more whitespace characters.

Example:

Assume that `words.txt` has the following content:

    the day is sunny the the
    the sunny is is

Your script should output the following, sorted by descending frequency:

    the 4
    is 3
    sunny 2
    day 1

Note:

- Don't worry about handling ties, it is guaranteed that each word's frequency count is unique.
- Could you write it in one-line using Unix pipes?