Chapter 9

1. Why do we need an exit status?
   So commands can signal to their callers if they succeeded or failed in a simple manner.
2. What is the difference between exit status, exit code and return code?
   An exit code and return code refer to the same thing. An exit status is a concept, which is brought to life by the exit/return code.

3. Which flag do we use with test to test for:
   • An existing directory
     -d
   • A writable file
     -w
   • An existing symbolic link
     -h (or -L)
4. What is the preferred shorthand syntax for test -d /tmp/?
   [[ -d /tmp/ ]]. Note that a space after [[ and before ]] is mandatory, or the command will fail!
5. How can we print debug information in a Bash session?
   Set the -x flag, either in the shell with set -x or when calling a script with bash -x.
6. How can we check if a variable has content?
   • if [[ -n ${variable} ]] to check if the variable is non-zero
   • if [[ ! -z ${variable...