git #

Prevent commits on a branch #

You can use a pre-commit hook to check the branch name to which you are commiting your changes. If you want to prevent direct changes to master create the following .git/hooks/pre-commit:

#!/bin/sh

# prevent commits on master
[ "$(git rev-parse --abbrev-ref --symbolic-full-name HEAD)" == "master" ] \
  && { echo "you shall not commit on master"; exit 1; }

Make sure the hook script is executable.

Merge Repositories #

I’ve had a few situations where I started front- and backend as two seperate projects but soon wished to track both in a single repository - as subdirectories. Last time I was in this situation, a stackoverflow answer proved most helpful. Here’s the gist:

Assume you have two repositories frontend and backend.

Prepare repositories #

First, you should move all files in each repository into a subdirectory to avoid merge conflicts and properly preserve commit history later. It would make sense to put all files in the frontend repository into a frontend subdirectory .. etc.

⦁ project/front : master= $ mkdir frontend
⦁ project/front : master= $ mv !(frontend) frontend/
⦁ project/front : master *%= $ git add .
⦁ project/front : master += $ git commit
[master c777b42] prepare frontend for merge
 65 files changed, 0 insertions(+), 0 deletions(-)
 [...]

Don’t forget about hidden files, as those are not moved by mv !(frontend) frontend/.

Do the same analogously for the backend or any other repository you want to merge.

Also, create a new repository to hold the merged projects. It helps to create an initial commit – even if completely empty – to indicate that unrelated histories were merged into each other.

⦁ project $ mkdir project && cd project
⦁ project/project $ git init
⦁ project/project : master # $ git commit --allow-empty

Add and fetch remotes #

Add all prepared repositories as remotes and fetch them.

⦁ project/project : master $ git remote add -f frontend ../frontend
⦁ project/project : master $ git remote add -f backend ../backend
...

Merge the repositories #

Finally, merge all those remotes into the combined project. Simply repeat this step for every remote you want to merge. At this point it pays off to prepare the repositories in order to avoid any merge conflicts right away.

⦁ project/project : master $ git merge -s ours --no-commit --allow-unrelated-histories frontend/master
Automatic merge went well; stopped before committing as requested
⦁ project/project : master|MERGING $ git read-tree --prefix= -u frontend/master
⦁ project/project : master +|MERGING $ git commit -a
[master 96012d4] Merge remote-tracking branch 'frontend/master'

You will end up with a repository where history looks somewhat like this:

⦁ project/project : master $ git log --graph
*   7a53ff5 2019-02-19 11:28:15 +0100 N Merge remote-tracking branch 'backend/master' (HEAD -> master) [Anton Semjonov]
|\
| * f89bfa3 2019-02-18 16:57:07 +0100 N prepare backend for merge (backend/master) [Anton Semjonov]
| * ea8a4f7 2018-09-18 15:19:16 +0200 N update scripts [Anton Semjonov]
| [...]
*   96012d4 2019-02-19 11:27:49 +0100 N Merge remote-tracking branch 'frontend/master' [Anton Semjonov]
|\
| * c777b42 2019-02-18 16:57:56 +0100 N prepare frontend for merge (frontend/master) [Anton Semjonov]
| * e3812e2 2019-01-18 22:35:30 +0100 N korrigiere Leonhard [Anton Semjonov]
| [...]
* b0605af 2019-02-19 11:25:36 +0100 N prepare combined repository for project [Anton Semjonov]

Mirror a Repository #

You can add pre- or post-receive hooks to bare repositories, which are executed whenever new commits are pushed. My original usecase was for my local GitLab installation to mirror everything to publicly available GitHub repositories. GitLab now provides this option in its Web interface.

The gist is this:

• Grant access to the git user via deploy keys on GitHub
• Add the GitHub repository as a remote to the bare repository
• Add a post-receive hook to mirror any changes

Granting access is a little bit out of the scope here but should be easily achievable with the above link. You can check the access with sudo -u git ssh git@github.com.

Then find the directory of the bare repository on your local machine. Copy the link to your public repository and add it as a remote:

git remote add --mirror=push mirror git@github.com:username/mirror.git

Finally add the following script as post-receive in hooks/ and mark it executable:

#!/bin/sh
exec git push --quiet "mirror" &

Now, every time you push to your local repository this script is executed and the repository will be mirrored.

Sign Commits with SSH Keys #

See Caleb Hearth’s Signing Git Commits with Your SSH Key.

The tl;dr is that you need to configure gpg.format to ssh and set user.signingKey to your SSH public key. Ideally, the key should be available in an SSH agent.

For verification, you need to create a file of the format <userid> <pubkey> and set its path in gpg.ssh.allowedSignersFile. You can use multiple comma-separated emails or an asterisk for the userid.

In the snippet below, I commented the commit.gpgSign key, because you can also sign each individual commit with git commit -S ... instead of just always signing everything.

[commit]
#  gpgSign = true
[gpg]
  format = ssh
[gpg.ssh]
  allowedSignersFile = ~/.ssh/git-trusted-keys
[user]
  signingKey = ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAID2Cxtc/CfWaSu4ybLqs3DTc9r0nEbyRS310fMqxYRZB