Lowercase head behaves differently in git worktrees

Today I discovered that referencing HEAD in git commands should technically always be uppercase.

On case-insensitive file systems you can use lowercase head most of the time and it just works… as long as you don’t use worktrees.

If you use head while in a worktree then it resolves to the head of the main worktree and not the head of the worktree you’re currently in like you would expect.

I learned this the hard way after getting some very confusing results from the git command I was running.

This Stackoverflow answer explains exactly why it happens and gives the very sensible advice to “Avoid this bad habit: if you don’t like typing HEAD in all uppercase, use @”.