How to fork a single branch of a repo, preserving commit log

fork-a-branch.sh

mkdir target-repo
cd target-repo
git init
git remote add origin git@github.com...
git remote add upstream git@github.com....
git fetch upstream
git pull upstream master
git push origin master

Alternative:

git clone git@github.com...
cd target-repo
git remote add upstream git@github.com....
git fetch upstream
git pull upstream master
git push origin master