git-update-ref

Delete a ref, useful for soft resetting the first commit

$ git update-ref -d [HEAD]

$ git update-ref -m [message] [HEAD] [4e95e05]

git update-ref [-m <message>] [--no-deref] <ref> <newvalue> [<oldvalue>]

[-m <message>]
    Use the given <message> to update the reflog. It will be ignored if the reflog entry would describe the same state transition as the previous one. The message is optional. If not specified, a generic message is used.

[--no-deref]
    Update the ref directly, rather than following symbolic refs. That is an update to refs/HEAD is not an update to .git/HEAD.

<ref>
    The name of the ref to update.

<newvalue>
    The new object name for the ref. Must be a valid object name or 'delete' to remove the ref.

[<oldvalue>]
    The expected old object name for the ref. If the ref does not contain this value, the update will fail. If <oldvalue> is specified as "", the update will fail if the ref does exist. If <oldvalue> is specified as a string that is all zeros, then the update will fail if the ref does not exist.

The git-update-ref command is a low-level plumbing command used to update, create, or delete references (refs) in a Git repository. Refs are pointers to Git objects (usually commits). It allows direct manipulation of the ref namespace, which can be useful for scripting and advanced Git workflows. The command performs atomic updates when possible, ensuring that the ref is updated consistently and avoiding race conditions.
It is generally safer to use higher-level porcelain commands like 'git branch', 'git tag', and 'git reset' for common operations. Directly manipulating refs can lead to repository corruption if not done carefully. The main purpose of this command is to update, create or delete references. The update is done by replacing the old object name stored in a ref with a new object name. It is used internally by other Git commands and can be used in scripts when precise control over ref updates is needed. The command supports both symbolic and direct ref updates. Symbolic refs point to other refs, while direct refs point to objects.

Directly manipulating refs can lead to repository corruption if not done carefully. Always double-check your commands and ensure you understand the implications of your actions before using this command. It is generally safer to use higher-level porcelain commands like 'git branch' or 'git reset' for common operations.

The command exits with a non-zero status if the update fails. This can be due to various reasons, such as an invalid object name, the ref not containing the expected old value, or a race condition. It is crucial to check the exit status of the command in scripts to ensure the update was successful.

git update-ref attempts to perform atomic updates when possible. This means that the update of the ref either succeeds completely or fails completely, preventing the ref from being left in an inconsistent state. This is particularly important in concurrent environments where multiple processes might be trying to update the same ref simultaneously.

git-branch(1), git-tag(1), git-reset(1), git-symbolic-ref(1)