Advice at a higher level: don’t try too hard to handle error cases in your scripts.

The best shell scripts are a list of imperative instructions to get something done. If an error occurs, bail as early as possible and with a useful message. Don’t try any harder than that.

For example:

  if ! complex_function
  then
    handle_error
  fi 

…doesn’t work as you’d expect because the “if” context changes the rules of set -e in complex_function. It’s much better to have complex_function crash your script with a helpful error message that the operator can ameliorate.

You may have a clever way of solving this problem, but the cleverer your solution gets, the further you diverge from the core language of shell scripting. You will suffer the lisp/Ruby problem of every script being in its own unique language that’s based on but not identical to the language with which your colleagues are familiar.

One shouldn't dismiss shell scripts completely – the command line is the primary interface to Unix and with more and more idempotent commands showing up every year ("ip route replace") it only gets easier to write simple, imperative lists of commands.