git-read-tree

git read-tree [-m] [--reset] [-u] [--prefix=] ...

-m
    Perform a merge, not just a reset. If multiple trees are provided, they will be merged together.

--reset
    Similar to -m, but empties the index before reading the tree(s). Useful for creating a new index from scratch.

-u
    After reading the tree(s) into the index, update the working directory to match. This is similar to git checkout but only updates the files that have changed.

--prefix=
    Read the tree(s) into a subdirectory of the index. The given prefix is prepended to all pathnames in the tree(s).


    Specifies the tree object(s) to read into the index. Multiple tree objects can be specified for merging.

git-read-tree
This command allows you to replace the contents of your index with a tree object without checking out any files. It is often used in conjunction with other Git commands like git-merge-index or git-checkout-index to manipulate the staging area. It can merge multiple trees by specifying multiple tree objects. The index is updated to reflect the provided trees. It is crucial for scripts and plumbing commands that need fine-grained control over the index and working directory. It differs from git checkout in that it does not update the working directory; it only modifies the staging area. Options allow specifying different merge strategies if multiple trees are specified. By default, it simply overlays the contents of trees specified later in the command line. This behavior can be controlled using merge strategies or specific path filtering.

When using the -m option with multiple trees, git-read-tree uses a simple overlay merge strategy by default. Trees listed later will overwrite entries from earlier trees if they conflict. More sophisticated merge strategies might be implemented using external merge tools or scripts with git merge-index.

It's crucial to understand the current state of your index before using git-read-tree. The command will overwrite the index's contents, so ensure that any uncommitted changes are either stashed or committed to avoid data loss. When using the command with the --reset option, it is even more critical to ensure nothing will be lost because the index will be emptied before adding new content.

git checkout(1), git merge-index(1), git checkout-index(1), git update-index(1)