The git-checkout command can be used to update specific files or directories in your working tree with those from another branch, without merging in the whole branch. This can be useful when working with several feature branches or using GitHub Pages to generate a static project site.
The git-checkout manual page describes how the git checkout command is not just useful for switching between branches.
When <paths> or --patch are given, git checkout does not switch branches. It updates the named paths in the working tree from the index file or from a named <tree-ish> (most often a commit)…The <tree-ish> argument can be used to specify a specific tree-ish (i.e. commit, tag or tree) to update the index for the given paths before updating the working tree.
In git, a tree-ish is a way of referring to a particular commit or tree. This can be a partial sha or the branch, remote, and tag name pointers.
The syntax for using git checkout to update the working tree with files from a tree-ish is as follows:
git checkout [-p|--patch] [<tree-ish>] [--] <pathspec>…
Therefore, to update the working tree with files or directories from another branch, you can use the branch name pointer in the git checkout command.
git checkout <branch_name> -- <paths>
As an example, this is how you could update your gh-pages branch on GitHub (used to generate a static site for your project) to include the latest changes made to a file that is on the master branch.
# On branch master
git checkout gh-pages
git checkout master -- myplugin.js
git commit -m "Update myplugin.js from master"
The need to update my gh-pages branch with specific files from my master branch was how I first found out about the other uses of the checkout command. It’s worth having a read of the rest of the git-checkout manual page and experimenting with the options.