Here's my inverse of the black friday sales - you can buy my book for £5 OR…get this…OR! You can _pay more_ if you think that's too little: 
Ko-fi
Working the Command Line: ebook - Remy Sharp's Ko-fi Shop
Don’t fear the terminal. No, really. However you’ve wound up face-to-face with the cool glow of a terminal window, Remy Sharp is here to help. ...