70 lines
2.7 KiB
Markdown
70 lines
2.7 KiB
Markdown
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---
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title: "Separate files from git repo into a submodule"
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date: 2023-02-22T20:31:34-05:00
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topics: ["git", "software development"]
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---
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I recently had a situation where a library I was working on, originally as part of one project, was going to be needed for another project.
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The ideal way to handle this situation, is to have the library files as their own git repo which is then added to the projects as a submodule.
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This way any changes required to the submodule for the needs of each project can be shared easily.
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It took me much longer than I would've liked to, but I finally managed to find the solution and wanted to share it with anyone else who might need it.
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Assume I have a git repo as below:
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```
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test
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├── README.md
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├── main.cpp
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├── test.cpp
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└── test.h
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```
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If I wanted to pull out the test.cpp and test.h files on their own with all the history for only those commits, the command is:
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```
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$ git filter-branch --force --prune-empty --index-filter \
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'git rm --cached --ignore-unmatch $(git ls-files | grep -v "test.h\|test.cpp")'
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```
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A couple notes should be mentioned.
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First when you run the git filter-branch command it will give you a message saying that you shouldn't use filter-branch and should instead use filter-repo.
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I don't know how to do this with filter-repo and didn't have the time to figure it out.
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The `--prune-empty` flag deletes all the commits that aren't associated with the files of interest so that you don't have to do a rebase.
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Finally to specify the files you want, you need to pass them to the grep command as:
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```
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grep -v "file1\|file2\|file3"
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```
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The `-v` flag inverts the match, returning all files to the `git rm` command which don't match the files you specify.
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The file names must be separated with `\|` for matching multiple different tokens.
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Once this command completes, you should be left with just the files of interest and the associated history.
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All that's left is simply setting a new remote url and then push, i.e.
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```
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$ git remote set-url origin submodule.git.url
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$ git push
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```
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**Final Important Note:** If this goes wrong you may get worried as all of your git history is wiped out.
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To fix this you can use `git reflog`.
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If you run `git reflog` after you mess up the `git filter-branch` you should see something like this (dummy commits from my fake repo):
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```
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$ git reflog
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790c883 (HEAD -> master) HEAD@{0}: filter-branch: rewrite
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3b3c8b8 HEAD@{1}: commit: Update test library
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93cfbd4 HEAD@{2}: commit: Add main function
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18259bc HEAD@{3}: commit: README update
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aba8323 HEAD@{4}: commit: init test files
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```
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You can then reset your git repo to a state before your filter branch command by running:
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```
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$ git reset --hard HEAD@{1}
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```
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Hopefully this helps someone out!
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