You’ve already used the STDIO redirection operators: <, >, 2>, 2>&1, and so on. You may also have used the appending operators: >> and 2>>, and maybe the most modern ones: &> and &>>, to redirect both STDOUT and STDERR at the same time.

These operators cover most of what you need day-to-day. But have you ever wondered what they actually do — why > affects output, < affects input, and 2> affects errors? The answer is file descriptors, and understanding them turns a collection of punctuation into a coherent system.