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# Git mirror
Run this script to synchronize a repository once.
## Dependencies
* bash
* git
* Tor and torify (see section "Tor")
## Usage
```
./git-mirror.sh <workdir> <leader> <follower...>
```
## Get started
Create a git repo, add remotes for the leader and the followers:
```bash
mkdir ~/git-mirror-my-repo; cd ~/git-mirror-my-repo
git init
git remote add github https://github.com/interesting/repo
git remote add gitea ssh://git@git.example.org/me/interesting-repo
git remote add gitlab ssh://git@git.example.com/myself/interesting-repo
```
Make sure Tor is running (see section "Tor"). Then run the mirroring script:
```bash
cd
git clone https://git.zeus.gent/midgard/git-mirror.git; cd git-mirror
./git-mirror.sh ~/git-mirror-my-repo github gitea gitlab
```
The first remote, github is the leader. The others are followers that are updated.
## Tor
The leader is fetched over Tor through torify. Make sure Tor is running, or edit the script,
changing `torify git fetch` into `git fetch`.
## Motivation
GitHub has always been hypocritical, promoting open source while keeping its own stack closed. When
GitHub was bought by Microsoft, the author decided to stop using it. Unfortunately a lot of
software still only has a presence on GitHub. To make it easier to work with those, this simple
mirror script was written.

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#!/bin/bash
set -euo pipefail
IFS=$'\n'
if [[ $# -lt 3 ]]; then
echo "Usage: $0 <workdir> <leader> <follower...>"
exit 1
fi
cd "$1"
leader="$2"
shift 2
followers=( "$@" )
echo "Working directory: $PWD"
echo "Leader remote: $leader"
echo "Follower remotes: ${followers[*]}" | tr '\n' ' '
echo; echo
torify git fetch --prune --multiple "$leader"
git fetch --prune --multiple "${followers[@]}"
echo
echo "Leader remote information:"
git remote show -n "$leader"
echo
echo "Follower remotes information:"
git remote show -n "${followers[@]}"
echo
branches=( $(git show-ref | sed -n 's| refs/remotes/'"$leader"'/|\t|p') )
echo -e "${#branches[*]} branches at leader:"
echo "${branches[*]}"
IFS=$'\t'
errors=( )
error() {
echo "XXX $1" >&2
errors[${#errors[*]}]="$1"
}
for branchspec in "${branches[@]}"; do
set $branchspec
leader_sha="$1"
branch="$2"
for remote in "${followers[@]}"; do
echo
echo "Updating $remote/$branch"
# Prepare state to push
follower_ref="refs/remotes/$remote/$branch"
if ! git show-ref --verify --quiet "$follower_ref"; then
echo "Branch doesn't exist yet at remote, creating"
git reset --hard "$leader_sha" --
else
echo "Branch existed at remote, updating"
git reset --hard "$follower_ref" --
git merge --ff-only "$leader_sha" || { error "$remote $branch: FF not possible"; continue; }
fi
git push "$remote" "+HEAD:$branch" || { error "$remote $branch: failed to push"; continue; }
done
done
if [[ "${#errors[*]}" -ge 0 ]]; then
echo "Errors:"
echo "${errors[@]}"
else
echo "No errors."
fi