Another utility that I find helpful is tac. It’s like cat, but in reverse. You can use it to reverse the lines in a file.
$ cat foo.txt
$ tac foo.txt
Oh, and also sort -R to shuffle lines in a file.
One of my favorite things about Vim is that you can pipe out a portion of your file to these utilities.
:'<,'> !sort -R
:'<,'> !tr -d '[:lower:]'
This is a pretty comprehensive reference. It’s nice to see tutorials focused on real life usage rather than man-page usage. It even introduces xargs as a combinator. Nice work!