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Note about SHA-1 values in the HEAD file #1259

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Jun 1, 2019
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Note about SHA-1 values in the HEAD file #1259

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8 changes: 6 additions & 2 deletions book/10-git-internals/sections/refs.asc
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Expand Up @@ -70,8 +70,12 @@ When you run commands like `git branch <branch>`, Git basically runs that `updat
The question now is, when you run `git branch <branch>`, how does Git know the SHA-1 of the last commit?
The answer is the HEAD file.

The HEAD file is a symbolic reference to the branch you're currently on.
By symbolic reference, we mean that unlike a normal reference, it doesn't generally contain a SHA-1 value but rather a pointer to another reference.
Usually the HEAD file is a symbolic reference to the branch you're currently on.
By symbolic reference, we mean that unlike a normal reference, it contains a pointer to another reference.

However in some rare cases the HEAD file may contain the SHA-1 value of a git object.
This happens when you checkout a tag, commit, or remote branch, which puts your repository in https://git-scm.com/docs/git-checkout#_detached_head["detached HEAD"] state.

If you look at the file, you'll normally see something like this:

[source,console]
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