Merge completely different Git repositories

merge.sh

#!/usr/bin/env bash

# https://stackoverflow.com/questions/1425892/how-do-you-merge-two-git-repositories
# https://stackoverflow.com/questions/2949738/git-merge-different-repositories
# https://git-scm.com/docs/git-filter-branch
# https://gist.github.com/msrose/2feacb303035d11d2d05

set -e

repos=(comp fun karen kvm learn logic m8080 mios mm study sugar tt)
branches=(main master master master master main master master master main master master)

for repo in "${repos[@]}"; do
  [ ! -d "$repo" ] && git clone "https://github.com/pedrominicz/$repo.git"
done

rm -rf a
mkdir a
cd a

git init -b main

for i in "${!repos[@]}"; do
  repo="${repos[i]}"
  branch="${branches[i]}"

  git remote add "$repo" "../$repo"
  git fetch "$repo" --tags
  git switch --orphan "$repo"
  git merge --allow-unrelated-histories --no-commit "$repo/$branch"
  FILTER_BRANCH_SQUELCH_WARNING=1 git filter-branch --force --index-filter "git ls-files --stage |sed \"s;\t;\t$repo/;\" |GIT_INDEX_FILE=\$GIT_INDEX_FILE.new git-update-index --index-info && mv \$GIT_INDEX_FILE.new \$GIT_INDEX_FILE" HEAD
  git remote remove "$repo"
done

git switch --orphan main

for repo in "${repos[@]}"; do
  git merge --allow-unrelated-histories --no-edit "$repo"
done

echo 'done'