Check if local git repo is ahead/behind remote

For future reference. As of Git v2.17.0

git status -sb

contains the word behind . So that can be used directly to check for pulls.

Note: Remember to run git fetch before running git status -sb

You can do this with a combination of git merge-base and git rev-parse. If git merge-base <branch> <remote branch> returns the same as git rev-parse <remote branch>, then your local branch is ahead. If it returns the same as git rev-parse <branch>, then your local branch is behind. If merge-base returns a different answer than either rev-parse, then the branches have diverged and you'll need to do a merge.

It would be best to do a git fetch before checking the branches, though, otherwise your determination of whether or not you need to pull will be out of date. You'll also want to verify that each branch you check has a remote tracking branch. You can use git for-each-ref --format='%(upstream:short)' refs/heads/<branch> to do that. That command will return the remote tracking branch of <branch> or the empty string if it doesn't have one. Somewhere on SO there's a different version which will return an error if the branch doesn't haven't a remote tracking branch, which may be more useful for your purpose.

In the end, I implemented this in my C++11 git-ws plugin.

string currentBranch = run("git rev-parse --abbrev-ref HEAD"); bool canCommit = run("git diff-index --name-only --ignore-submodules HEAD --").empty();bool canPush = stoi(run("git rev-list HEAD...origin/" + currentBranch + " --ignore-submodules --count")[0]) > 0;

Seems to work so far. canPull still needs to be tested and implemented.

Explanation:

• currentBranch gets the console output, which is a string of the current branch name
• canCommit gets whether the console outputs something (difference between current changes and HEAD, ignoring submodules)
• canPush gets the count of changes between origin/currentBranch and the local repo - if > 0, the local repo can be pushed