Last Updated: 2024-03-05
I used the virtual machine Vagrant in a project and wanted to add some code that made a change (appended a line to file) only the first time the script was run, but not afterwards - idempotency of sorts.
The trick is to create a new file whose sole purpose is signifying "work has been done" after first execution, and then check for that file on subsequent runs - using its presence/absence to switch out logic.
if [ ! -f ~/.homestead_post_install_customisations_done ]; then
# Add one time setup customisation
echo "Installing setup customizations"
# IMPORTANT: The version number for postgres will change over time,
# potentially breaking this script.
echo "host all all 0.0.0.0/0 md5" | sudo tee -a /etc/postgresql/12/main/pg_hba.conf
sudo service postgresql restart
echo "Already made customizations"