move-files-with-history.sh

#!/bin/bash

# set the env variables .. OLDREPO=git@github.com:user/repo.git, etc
# Files is a small regex of all the files you want to move
# FILES='example.txt|/*.png' , etc

export OLDREPO
export TARGETREPO
export FILES

# clone the old repo into a old-repo directory
git clone $OLDREPO ~/old-repo && cd ~/old-repo
git checkout -b files-to-move

# filter the history down to just the files you are moving
git filter-branch -f --prune-empty --index-filter 'git ls-files | grep -v -E "$FILES" | xargs git rm --cached --ignore-unmatch' HEAD

# clone the target repo, add old-repo as a remote
# pull the files in
git clone $TARGETREPO ~/new-repo && cd ~/new-repo
git checkout -b new-files
git remote add here ~/old-repo/.git 
git pull here files-to-move --allow-unrelated-histories

# git add . 
# git commit -m "New files"
# now ready to merge into master of new repo

# OPTIONAL: if you want to remove the files from the old repo
cd ~/old-repo
git pull origin master --allow-unrelated-histories
git filter-branch -f --prune-empty --index-filter 'git ls-files | grep -E "$FILES" | xargs git rm --cached --ignore-unmatch' HEAD
git branch -D files-to-move