Merge Remote Branch without Checkout

If we are checked out on a branch and want to merge a remote branch to some different branch without leaving the current branch, we can do the following:

git fetch <remote> <sourceBranch>:<destinationBranch>

Here, we are fetching the remote branch <sourceBranch> from <remote> and merging it to <destinationBranch>.

sourceBranch and destinationBranch can be the same. For example, if you are checked out on develop and want to merge remote updates from master to develop without leaving develop, you can do the following:

git fetch origin master:master
git merge master

Source: Merge, update, and pull Git branches without using checkouts