Comment by twooster

You should almost always be running Bash in `-e` (exit-on-error) mode. This necessitates precisely the construct mentioned in this article.

For example:

  set -e

  var="$( false )"
  if [ $? -eq 0 ] ; then
    echo Ok: "$var"
  else
    echo Not ok: $?
  fi

If you run this program, neither "Ok" or "Not ok" will be echoed, because the program will exit with an error on the `var=` line. (Not to mention the $? on the not-ok line won't work because it will be the exit code of the `[` test command in the conditional, not the exit code of the captured subshell command).

Instead the following will work:

  set -e

  if var="$( false )" ; then
    echo Ok: "$var"
  else
    echo Not ok: $?
  fi

Note that this will _not_ work:

  if ! var="$( false )"; then
    echo Not ok: $?
  fi

Your output will be "Not ok: 0". This is because negation impacts the exit code of the previous command.