Git – How to Reference Branch Start Commit

commitgitreference

I am trying to find how to reference branch start commit from script. I mean the commit sha at which branch was forked.

Moreover I expect it work for history made from svn repo.

This post just gives first commit of repo creation and not feature branch start commit.

Best Answer

What you're looking for is the command merge-base:

git merge-base master feature-branch

will print the best common ancestor of those two branches, i.e. where they forked apart. (The documentation has pretty pretty pictures to clarify some of the interesting cases)

An additional tidbit is you can add the merge-base flag --fork-point to automatically include the name feature-branch, read more in this answer.

Related Solutions

Git – How to Reference the Initial Commit

Do not use git-log for scripting: use either git-rev-list, or git-log with specified custom format (--format=*<sth>* option).

There is additional problem with your question: there can exist more than one such TAIL root commit (parentless commit) in a repository (even if we discount disconnected branches, such as 'html', 'man' and 'todo' in git.git repository). This is usually result of joining separate projects in one, or using subtree merge of separately developed subproject.

For example git repository has 6 root commits: git-gui, gitk (subtree-merged), gitweb (merged in, no longer developed separately), git mail tools (merged very early in project history), and p4-fast-export (perhaps accidental). That is not counting roots of 'html and 'man' branches, "convenience" branches which contains pre-generated documentation, and 'todo' branch with TODO list and scripts.

If you have git 1.7.4.2 or newer, you can use the --max-parents option:

$ git rev-list --max-parents=0 HEAD

Otherwise, you can get list of all parentless (root) commits accessible from current branch using:

$ git rev-list --parents HEAD | egrep "^[a-f0-9]{40}$"

Git – How to Point Branch to New Commit

Solution

git checkout master
git merge C

With C being the SHA1 of commit C.

Result

                 D (dev)
                /
master A - B - C (move master HEAD)

It should be a fast-forward merge.