Looking through the examples, I see lots of pitfalls such as unquoted variables, backticks, no error checking, and parsing ls. Also bash features such as [[ are

Looking through the examples, I see lots of pitfalls such as unquoted variables, backticks, no error checking, and parsing ls. Also bash features such as [[ are ignored, and expr is sometimes used for what bash handles natively. Also there's a lot of new stuff that this old guide doesn't cover.