Git: Find the nearest ancestor branch

git-ancestor.sh

# 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?"

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 )}'