This is part of the Semicolon&Sons Code Diary - consisting of lessons learned on the job. You're in the algorithms category.
Last Updated: 2023-03-28
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 touch ~/.homestead_post_install_customisations_done else echo "Already made customizations" fi