See the size of a directory in your terminal

Say you quickly want to check the size of your current directory, in a human readable way. We can easily check that out using the du command. Per the UNIX man page, du's purpose is to "estimate file space usage". If we add the -s flag, which prints a summary (rather than stats for individual files) and the -h flag, which prints sizes in a human readable format (ex. 1K, 234M, or 4.8G), we get a wonderful output

$ du -sh
  19M    .

The du command takes files and folders as arguments, and will use the current directory as the target if none is specified. This means that you can see the size of a certain file or directory if you'd like

$ ls
  Gemfile app.rb
$ du -sh Gemfile
  4.0K    Gemfile