125 lines
4.2 KiB
Markdown
125 lines
4.2 KiB
Markdown
---
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title: About Git subtree merges
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redirect_from:
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- /articles/working-with-subtree-merge
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- /subtree-merge
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- /articles/about-git-subtree-merges
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- /github/using-git/about-git-subtree-merges
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- /github/getting-started-with-github/about-git-subtree-merges
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- /github/getting-started-with-github/using-git/about-git-subtree-merges
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intro: 'If you need to manage multiple projects within a single repository, you can use a *subtree merge* to handle all the references.'
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versions:
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fpt: '*'
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ghes: '*'
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ghec: '*'
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---
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## About subtree merges
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Typically, a subtree merge is used to contain a repository within a repository. The "subrepository" is stored in a folder of the main repository.
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The best way to explain subtree merges is to show by example. We will:
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* Make an empty repository called `test` that represents our project.
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* Merge another repository into it as a subtree called `Spoon-Knife`.
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* The `test` project will use that subproject as if it were part of the same repository.
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* Fetch updates from `Spoon-Knife` into our `test` project.
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## Setting up the empty repository for a subtree merge
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{% data reusables.command_line.open_the_multi_os_terminal %}
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1. Create a new directory and navigate to it.
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```shell
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mkdir test
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cd test
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```
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1. Initialize a new Git repository.
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```shell
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$ git init
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> Initialized empty Git repository in /Users/octocat/tmp/test/.git/
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```
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1. Create and commit a new file.
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```shell
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$ touch .gitignore
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$ git add .gitignore
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$ git commit -m "initial commit"
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> [main (root-commit) 3146c2a] initial commit
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> 0 files changed, 0 insertions(+), 0 deletions(-)
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> create mode 100644 .gitignore
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```
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## Adding a new repository as a subtree
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1. Add a new remote URL pointing to the separate project that we're interested in.
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```shell
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$ git remote add -f spoon-knife https://github.com/octocat/Spoon-Knife.git
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> Updating spoon-knife
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> warning: no common commits
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> remote: Counting objects: 1732, done.
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> remote: Compressing objects: 100% (750/750), done.
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> remote: Total 1732 (delta 1086), reused 1558 (delta 967)
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> Receiving objects: 100% (1732/1732), 528.19 KiB | 621 KiB/s, done.
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> Resolving deltas: 100% (1086/1086), done.
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> From https://github.com/octocat/Spoon-Knife
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> * [new branch] main -> Spoon-Knife/main
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```
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1. Merge the `Spoon-Knife` project into the local Git project. This doesn't change any of your files locally, but it does prepare Git for the next step.
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If you're using Git 2.9 or above:
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```shell
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$ git merge -s ours --no-commit --allow-unrelated-histories spoon-knife/main
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> Automatic merge went well; stopped before committing as requested
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```
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If you're using Git 2.8 or below:
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```shell
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$ git merge -s ours --no-commit spoon-knife/main
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> Automatic merge went well; stopped before committing as requested
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```
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1. Create a new directory called **spoon-knife**, and copy the Git history of the `Spoon-Knife` project into it.
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```shell
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$ git read-tree --prefix=spoon-knife/ -u spoon-knife/main
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> fatal: refusing to merge unrelated histories
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```
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1. Commit the changes to keep them safe.
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```shell
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$ git commit -m "Subtree merged in spoon-knife"
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> [main fe0ca25] Subtree merged in spoon-knife
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```
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Although we've only added one subproject, any number of subprojects can be incorporated into a Git repository.
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> [!TIP]
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> If you create a fresh clone of the repository in the future, the remotes you've added will not be created for you. You will have to add them again using [the `git remote add` command](/get-started/git-basics/managing-remote-repositories).
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## Synchronizing with updates and changes
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When a subproject is added, it is not automatically kept in sync with the upstream changes. You will need to update the subproject with the following command:
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```shell
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git pull -s subtree REMOTE-NAME BRANCH-NAME
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```
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For the example above, this would be:
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```shell
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git pull -s subtree spoon-knife main
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```
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## Further reading
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* [The "Advanced Merging" chapter from the _Pro Git_ book](https://git-scm.com/book/en/v2/Git-Tools-Advanced-Merging)
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* [How to use the subtree merge strategy](https://www.kernel.org/pub/software/scm/git/docs/howto/using-merge-subtree.html)
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