How to pragmatically check with bash script if a branch in git needs to be rebased? -

i'm working on bash script team enforce regular rebasing of working branches. problem facing @ moment how determine whether branch behind master and/or if needs rebased, rather blindly attempting rebase branch.

here simplified version of have far:

#process each repo in working directory. repo_dir in $(ls -1);     # if working branch clean ...          # begin update of local master         git checkout master         git fetch origin         git merge remotes/origin/master         # end update of local master          sync_branch in $(git branch | cut -c 3-);             if [ "$sync_branch" != "master" ];                 # begin rebase working branch                 git checkout $sync_branch                 git rebase master                 # not push working branch remote.                 # end rebase working branch             fi         done     fi done 

any ideas appreciated. thanks!

to tell if need rebase branch, need find out latest commit , last commit 2 branches share.

to find latest commit on branch:

git show-ref --heads -s <branch name> 

then find last commit branches have in common:

git merge-base <branch 1> <branch 2> 

now need find out if these 2 commits same commit. if are, don't need rebase. if not, rebase required.

example:

hash1=$(git show-ref --heads -s master) hash2=$(git merge-base master foo/bar) [ "${hash1}" = "${hash2}" ] && echo "ok" || echo "rebase required" 

though stated in comment, if attempt rebase branch date. git gracefully handle situation , exit.