How to check whether the remote repo has changed and I need to pull?
Now I use this simple script:
git pull --dry-run | grep -q -v 'Already up-to-date.' && changed=1
but it is rather heavy.
Do you know any better way? The ideal solution would check all the remote branches, and return names of the changed branches and the number of new commits in each one.
The command
git ls-remote origin -h refs/heads/master
will list the current head on the remote -- you can compare it to a previous value or see if you have the SHA in your local repo.
I think the best way to do this would be:
git diff remotes/origin/HEAD
Assuming that you have the this refspec registered. You should if you have cloned the repository, otherwise (i.e., if the repo was created de novo locally, and pushed to the remote), you need to add the refspec explicitly.
git remote update to bring your remote refs up to date. Then you can do one of several things, such as:
git status -uno will tell you whether the branch you are tracking is ahead, behind or has diverged. If it says nothing, the local and remote are the same.
git show-branch *master will show you the commits in all of the branches whose names end in master (eg master and origin/master).
If you use -v with git remote update you can see which branches got updated, so you don't really need any further commands.
However, it looks like you want to do this in a script or program and end up with a true/false value. If so, there are ways to check the relationship between your current HEAD commit and the head of the branch you are tracking, although since there are four possible outcomes you can't reduce it to a yes/no answer. However, if you're prepared to do a pull --rebase then you can treat "local is behind" and "local has diverged" as "need to pull", and the other two as "don't need to pull".
You can get the commit id of any ref using git rev-list --max-count=1 <ref>, so you can do this for master and origin/master and compare them. If they are equal, the branches are the same. If they're unequal, you want to know which is ahead of the other. Using git merge-base master origin/master will tell you the common ancestor of both branches, and if they haven't diverged this will be the same as one or the other. If you get three different ids, the branches have diverged.
To do this properly, eg in a script, you would need to get the name of the current branch, and the name of the remote branch it's tracking. Check out the bash prompt-setting function in /etc/bash_completion.d for ideas.
Run git fetch (remote) to update your remote refs, it's show you what's new. Then, when you checkout your local branch, it will show you whether it's behind upstream.