Writing re-runable shell script

I recently started playing with devstack again (An all-in-on OpenStack developer setup). Last time was over 3 years ago because I remember a pull request for a missing dependency at the time.

The installation docs provide information to bootstrap your system with a necessary user and privileges, however like many docs for software setup they contain one off instructions.

adduser stack
echo "stack ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers

When you write operations code you need to always be thinking about “testability” and “automation”. It is important to write re-runable code. You should always write parameterized code when possible, which can be refactored into usable functions at any time.

This is a good example to demonstrate a simple test condition for making the initial instructions re-runable.

sudo su -
# This creates default group of same username
# This creates user with default HOME in /home/stack
[ `grep ${NEW_USER} /etc/passwd | wc -l` -eq 0 ] && useradd -s /bin/bash -m ${NEW_USER}
[ ! -s ${NEW_USER_SUDO_FILE} ] && umask 226 && echo "${NEW_USER} ALL=(ALL) NOPASSWD: ALL" > ${NEW_USER_SUDO_FILE}