Challenge with multiple GitHub accounts

There are several great articles giving advice on how to handle multiple GitHub accounts. The one I liked in particular has a pretty self-explanatory title: Automatically use correct SSH key for remote Git repo

I value the article for two main reasons:

1. It helped me solve my problem with the authentication agent
2. It gave me an idea of how to automate the process even further

Authentication Agent

If you are reading this, I’d assume you are way too familiar with ssh-add technicalities. The problem I failed to realise at first was a mere fact that the additional ssh key is not stored permanently. Once I restarted my laptop or even just the terminal, the key was gone and I was pulling my hair trying to understand why the heck I couldn’t push to the remote GitHub repo anymore (since I did add the damn key, right?!). Obviously, ssh-add -L or ssh-add -l give the ultimate proof of what identities is the agent aware of.

There is another superb blog post addressing specifically this issue. Once again, the title says it all: Permanently Add SSH key ssh-add. As a Mac user I simply relied on Keychain:

ssh-add -K ~/.ssh/id_rsa_PERSONAL

Automation

Once the identities are under control and your pushes start to work again, there is one tiny bit left to resolve. With multiple identities the hosts in GitHub SSH links need to be kept in sync with your local ssh config (~/.ssh/config). That requires changing the links manually. Here is what I mean:

GitHub says: git@github.com:YOU/YOUR_REPO.git

Your ssh config dictates:

Host 
personal

HostName github.com
 User git
 Hostname github.com
 PreferredAuthentications publickey
 Port 22
 IdentityFile 
~/.ssh/id_rsa_PERSONAL 

Therefore, if you want to see your pushes work, you have no choice but to change the provided link before you go and clone the repo:

git clone git@personal:YOU/YOUR_REPO.git

Smart, but tedious.

One obvious solution to this problem is to use a bash script which would do the appropriate adjustment and run the git clone on your behalf using the modified link. How would you do it though? The only distinction in the ssh config are different identities. Apart from that, all the specified hosts look the same.

Tom Atkins’ blog post gave me the idea of using comments as annotations. Tom suggests, let me quote:

#user1 account
Host github.com-user1
..
#user2 account
Host github.com-user2
..

Here is how I adopted his approach in my own config file:

Host 
work
 HostName github.com
 User git
 Hostname github.com
 PreferredAuthentications publickey
 Port 22
 IdentityFile ~/.ssh/id_rsa

Host 
personal
 HostName github.com
 User git
 Hostname github.com
 PreferredAuthentications publickey
 Port 22
 IdentityFile ~/.ssh/id_rsa_PERSONAL

As you can see, now I do have a direct mapping between my GitHub users and the relevant host names (work, personal). The script which swaps github.com for one of the two configured host names is still in its infancy. However, it works already (on my machine, LOL!). Check it out on GitHub.

Suppose I have a personal repo – a fork of one of the Coursera’s projects. instead of tweaking the ssh link by hand and running git clone, I rather keep the link as is and pass it to my script.

$./wrapper.sh git@github.com:zezutom/ExData_Plotting1.git

Checking the git config in the cloned project confirms the host name was replaced as expected:

$ cd ExData_Plotting1
$ cat .git/config
[core] ..
[remote "origin"]
  url = git@personal:zezutom/ExData_Plotting1.git
  fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
  remote = origin
  merge = refs/heads/master

Thanks for reading and stay tuned. Next time, I will talk you through the script in detail.