Tack the history of one repository onto another

Combine Histories.txt

# two repositories r1 and r2
# r2 was created by manually copying the files from r1 without preserving history
# so r2 and r1 don't have a common commit

git clone r2 work
cd work
git remote add r1 <path_to_r1>
git fetch r1
git checkout -b r1_master r1/master
git checkout master
git rebase -i r1_master

# change the first commit in the list from pick to edit
# now the rebase stops at the first commit in r2

rm -rf *

cd ../r2
git log # get the shaw of the first commit in r2
git checkout -b first <shaw_of_first_commit>
cp -r * ../work
cd ../work
git add *
git add -u
git rebase --continue

# clean up
git branch -d r1_master
cd ../r2
git checkout master
git branch -d first
cd ../work