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

Not sed and grep, but tr, sort, uniq, and awk:

% (tr ' ' '\n' | sort | uniq -c | awk '{print $2"@"$1}') <