Tech notes for git

Git: get the latest commit

This is easy enough git rev-parse HEAD.

git git-lastest-commit-hash

Git: Subtree basics

If you hate git submodule, then you may want to give git subtree a try.

Let's say you have a git repository init'd with at least one commit.

You can add another repository to this respository like this:

  1. First specify you want to add the subtree
  2. Then specify the prefix directory into which you want to pull
  3. Specify the remote repository
  4. Specify the remote branch
  5. Specify you want to squash all the remote repository's logs

In other words

git subtree add --prefix .vimrepo master --squash

This will clone into the directory .vimrepo.

If you want to pull in any new commits to the subtree from the remote, issue the same command as above, replacing add for pull:

git subtree pull --prefix .vimrepo master --squash

If you make a change to anything in .vimrepo the commit will be stored in the host repository and its logs.

That is the biggest change from submodules.

If you now want to update the subtree repository with that commit, you must run the came command as above, excluding --squash and replacing pull for push.

git subtree push --prefix .vimrepo master

I've only just starting playing, but my main problems so far:

  1. You can't easily list the subtrees in your project
  2. You can't, at least easily, list the remote repositories of the subtrees
  3. The logs are slightly confusing when you update the host repository with subtree commits, then push the subtree to its host, and then pull the subtree.

Other than that, they're looking nicer than submodules.

git git-subtree

Git: Create a patch file via git diff

If you run

git diff > your.patch

The normal git diff output will be saved to a file.

If you take that and apply it to the directory with patch, you'll update your files.

patch -p1 < your.patch

You need -p1 since in the diff output the file name are like


And you only need the 'your/directory/...' bit, so p1 says ignore everything up until after the first slash.

If you want to make backups, issue patch -p1 with the -b argument.

git git-diff unix unix-patch

Java: Using JGit to clone a repository



remoteRepo will be something like "" and dir is a File object stating where to put the new repository.

If the directory doesn't exist, you must create it with dir.mkdirs();

java git

Git: Checkout revisions past

If you want to checkout a file as it was one revision ago on the master branch:

 git checkout master~1 thedir/thefile.txt

I used this to remove an update to a file when amending a commit.

(I hadn't pushed to master, hence the ability to amend without screwing things up.)

git git-checkout

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