Agarwal - Command Line Text Processing with GNU Coreutils
    https://learnbyexample.github.io/cli_text_processing_coreutils/
    https://github.com/learnbyexample/cli_text_processing_coreutils
    https://leanpub.com/cli_coreutils
    https://learnbyexample.gumroad.com/l/cli_coreutils