Git HEAD

In Git, HEAD is a reference to the current branch or commit that the user is working on. It typically points to the most recent commit in the current branch, but can also point to other commits when working with detached HEAD states.

Purpose of HEAD

• Current Commit Reference: HEAD helps Git know where the current working directory is in relation to the commit history.
• Working Directory: HEAD allows Git to track changes relative to the last commit made on the active branch.
• Branch Switching: HEAD changes when you switch branches, as it always points to the tip of the branch you’re working on.

Viewing HEAD

To check the current commit or branch where HEAD is pointing, the following command can be used:

git log --oneline

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This shows a simplified log of the commit history, where the commit at the top is the one pointed to by HEAD.

Detached HEAD State

A detached HEAD occurs when HEAD is not pointing to the tip of a branch, but rather to a specific commit. In this state, changes are not linked to any branch.

For example, this command checks out a specific commit, causing HEAD to be detached from any branch:

git checkout <commit_hash>

Changes made in detached HEAD state won’t be associated with any branch unless explicitly created as a new branch. It can be useful for exploring past commits or making temporary changes.

Updating HEAD

HEAD is updated when switching branches, as it points to the latest commit of the newly checked-out branch:

git checkout develop

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This command switches the current branch to develop and HEAD points to the most recent commit on the develop branch.

Resetting HEAD

We can use git reset to move HEAD to a previous commit, changing the state of the working directory:

git reset --hard <commit_hash>

For example, this command resets HEAD to the commit with hash abc1234, and the working directory will match the state of that commit:

git reset --hard abc1234

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