Add a test to see what shell is running the script, and exit if it's not `zsh`

[BigMacAdmin]

Determine if it's possible/safe/reliable to add a test to see what shell is running the script, and exit with a loud error if it's not zsh

[BigMacAdmin]

if [ -z "${ZSH_VERSION}" ]; then
    # ZSH_VERSION is set automatically by zsh and only by zsh.
    # If it's empty or unset, we're running under the wrong shell.
    echo "Bad bad bad"
    exit 1
fi

LLM of choice is suggesting this.

[BigMacAdmin]

Opened an issue on Installomator as well, since this problem is common there: Installomator/Installomator#2882