git: copy files between branches

Frequently, I want to pull in just a single file from another git branch. I always need to look up the specifics, so I’m documenting it to hopefully make finding it easier in the future.

Imagine the following situation:

• You’re working on a feature branch feature/awesome-feature
• A teammate, working on feature/also-awesome just pushed changes to the index file in the src directory that you want to merge in.

To pull in those changes:

1. Confirm your remote repository is configured. Alternatively, if you’ve got a local copy of feature/also-awesome you can use that too.

   $ git remote -v
   origin git@git.remine.com:app-v2/repaint.git (fetch)
   origin git@git.remine.com:app-v2/repaint.git (push)

2. Checkout the file from the target branch

   git checkout origin/feature/also-awesome src/package-lock.json

   More generically, that’s:

   git checkout [target-branch] [path/to/file]

   Normally, when we use checkout, we’re checking out the entire branch, but what we’re doing here is taking advantage of the following options:

   ] [--] <pathspec Overwrite paths in the working tree by replacing with the contents in the index or in the <tree-ish> (most often a commit). When a <tree-ish> is given, the paths that match the <pathspec> are updated both in the index and in the working tree.

   The index may contain unmerged entries because of a previous failed merge. By default, if you try to check out such an entry from the index, the checkout operation will fail and nothing will be checked out. Using -f will ignore these unmerged entries. The contents from a specific side of the merge can be checked out of the index by using —ours or —theirs. With -m, changes made to the working tree file can be discarded to re-create the original conflicted merge result.

   ] [--] [<pathspec This is similar to the “check out paths to the working tree from either the index or from a tree-ish” mode described above, but lets you use the interactive interface to show the “diff” output and choose which hunks to use in the result. See below for the description of —patch option.

While I’m only checking out a single file, as the manual describes, the checkout command is capable of pulling in multiple. It just requires a separate path for each.