If you have various projects which used either "main" or "master" as the main branch, and also have a remote which uses the other naming (e.g. heroku or another PaaS), you might find yourself accidentally switching to the wrong branch name and working on it. Here's how to inhibit that.

Put this in .git/hooks/post-checkout

if [ `git branch --show-current` == "master" ]; then
  echo "DO NOT USE MASTER"
  git checkout main
  git branch -d master
fi

set it to executable:

chmod u+x .git/hooks/post-checkout

that's it!