Understanding the HEAD-file
In the context of Version-Control systems, specifically Git, the HEAD-file is a vital metadata file located within the .git directory of a repository. It functions as a pointer that identifies the current active Branch or the specific Commit that the Working-Directory currently reflects.
Under normal circumstances, the HEAD-file contains a symbolic reference to a branch. For example, it might contain the string ref: refs/heads/main. This tells Git that any new Commit created will be appended to the 'main' branch. When a developer uses the git checkout command to switch branches, Git updates the HEAD-file to point to the new branch's reference. Detailed specifications on this mechanism can be found in the Official Git Glossary and the Pro Git Book.
A unique state known as a Detached-HEAD occurs when the HEAD-file points directly to a specific SHA-1 hash rather than a named branch. This typically happens when checking out a specific historical Commit, a Tag, or a remote branch. While in this state, new commits are not associated with any branch and can become orphaned if the user switches back to a standard branch without creating a new reference.