Merging two Git repositories with unrelated branches

Suppose you have a Git repository for your Jekyll blog. Suppose you have another Git repository for your Octopress blog. Suppose you realize they have similar text content, and you prefer to have their branches in the same repository. How to merge the two repositories into one, while preserving the unrelated commit histories?

One way to do it:

Pick one of the repositories where you would like to have all branches. Let’s call this repository repoA, and the other one repoB.
For each branch you want to copy from repoB, create an orphan branch, remove all content from it, and merge from the branch in repoB.

Git commands:

# create a clean new clone of repoA
git clone url_to_repoA /tmp/work
cd /tmp/work

# register repoB and fetch its branches
git remote add repoB url_to_repoB
git fetch repoB

# create an unrelated (orphan) branch, wipe it clean, merge from repoB/master, and push to `origin`
git checkout --orphan other-master
git rm -fr .
git merge repoB/master
git push origin HEAD

Merging two Git repositories with unrelated branches —08 May 2014