Taken from http://www.davidpashley.com/articles/writing-robust-shell-scripts/

Bash_guidelines.rst

```bash
set -u   # The script crashes if a variable is uninitialized
set -e   # The script crashes if the exit code of a command is not zero
```

* Use ``"$@"`` instead of ``$@``
* Use quotes around filenames
* Use ``mkdir -p`` to create a full path
* Use ``rm || true `` to avoid a non-zero exit
* Use traps when using temporary files:
  ```bash
  if [ ! -e $lockfile ]; then
     trap "rm -f $lockfile; exit" INT TERM EXIT
     touch $lockfile
     critical-section
     rm $lockfile
     trap - INT TERM EXIT
  else
     echo "critical-section is already running"
  fi
  ```
* To avoid race conditions with lock files:
  ```bash
  if ( set -o noclobber; echo "$$" > "$lockfile") 2> /dev/null; then
  ```
* Implement rollback functions when modifying dangerous things:
  ```bash
  rollback() {
   del_from_passwd $user
   if [ -e /home/$user ]; then
      rm -rf /home/$user
   fi
   exit
  }

  trap rollback INT TERM EXIT
  add_to_passwd $user
  cp -a /etc/skel /home/$user
  chown $user /home/$user -R
  trap - INT TERM EXIT
  ```
* Be atomic : work on copies and if the work succeeded, copy the modified files back
* Never use [ or test, always use [[ for secure string handling
* [[ works only in Bash, Zsh and the Korn shell, and is more powerful; [ and test are available in POSIX shells
* Avoid using echo and use printf instead