How to find the nearest parent of a Git branch?

Question

Let\'s say I have the following local repository with a commit tree like this:

master --> a
            \\
             \\
      develop c --> d
               


        

Answer 1

A rephrasal

Another way to phrase the question is "What is the nearest commit that resides on a branch other than the current branch, and which branch is that?"

A solution

You can find it with a little bit of command line magic

git show-branch \
| sed "s/].*//" \
| grep "\*" \
| grep -v "$(git rev-parse --abbrev-ref HEAD)" \
| head -n1 \
| sed "s/^.*\[//" 

With awk:

git show-branch -a \
| grep '\*' \
| grep -v `git rev-parse --abbrev-ref HEAD` \
| head -n1 \
| sed 's/[^\[]*//' \
| awk 'match($0, /\[[a-zA-Z0-9\/-]+\]/) { print substr( $0, RSTART+1, RLENGTH-2 )}'

Here's how it works:

1. Display a textual history of all commits, including remote branches.
2. Ancestors of the current commit are indicated by a star. Filter out everything else.
3. Ignore all the commits in the current branch.
4. The first result will be the nearest ancestor branch. Ignore the other results.
5. Branch names are displayed [in brackets]. Ignore everything outside the brackets, and the brackets.
6. Sometimes the branch name will include a ~# or ^# to indicate how many commits are between the referenced commit and the branch tip. We don't care. Ignore them.

And the Result

Running the above code on

 A---B---D <-master
      \
       \
        C---E---I <-develop
             \
              \
               F---G---H <-topic

Will give you develop if you run it from H and master if you run it from I.

The code is available as a gist

Answer 2

You can also try:

git log --graph --decorate

Answer 3

Cross-platform implementation with Ant

    <exec executable="git" outputproperty="currentBranch">
        <arg value="rev-parse" />  
        <arg value="--abbrev-ref" />  
        <arg value="HEAD" />  
    </exec>

    <exec executable="git" outputproperty="showBranchOutput">
        <arg value="show-branch" />  
        <arg value="-a" />  
    </exec>

    <loadresource property="baseBranch">
      <propertyresource name="showBranchOutput"/>
          <filterchain>
            <linecontains>
              <contains value="*"/>
            </linecontains>
            <linecontains negate="true">
              <contains value="${currentBranch}"/>
            </linecontains>
            <headfilter lines="1"/>
            <tokenfilter>
                <replaceregex pattern=".*\[(.*)\].*" replace="\1"/>
                <replaceregex pattern="[\^~].*" replace=""/>
            </tokenfilter>
          </filterchain>
    </loadresource>

    <echo message="${currentBranch} ${baseBranch}" />