• .gitignore
• .git/info/exclude
• ~/.config/git/ignore

.gitignore

.gitignore is the usual file where you write files you want to ignore. It’s checked into Git along with the rest of the code. Whatever files you add to it will not get taken into account when running git commands.

.git/info/exclude

The exclude file lives in the .git directory of every Git repository but changes to it are not checked into Git. It usually has a few comment lines on a fresh Git repository. This file is useful for ignoring things on a per-repo basis. For example, you may have a personal notes.txt file in a repository that you don’t want to check into git but you also don’t want to add to .gitignore because it’s unique to your workflow. In that case you would add notes.txt to .git/info/exclude.

~/.config/git/ignore

The ignore file lives in your machine’s home directory in ~/.config/git/ignore. Whatever filenames are added to this file are ignored globally at a machine-level. This file is not checked into Git and isn’t associated with any particular repository. It’s a great place to add files that you want to ignore in every git repository on your computer. For example, if you’re on macOS, adding .DS_Store here would be ideal.

You can customize the global ignore file to be a different file. For example, if you want your global git ignore file to be .gitignore_global you would run the command:

git config --global core.excludesFile ~/.gitignore_global

And if you ever want to return to the default setting, run:

git config --global --unset core.excludesFile

Checking Which File Is Ignoring a Specific File

When adding filenames to any of these, you can use this command to check how a filename is being ignored. For example, if you want to check how .DS_Store is being ignored, run git check-ignore -v .DS_Store in any Git repository.

Here is the output when the repository’s .gitignore is ignoring .DS_Store:

$ git check-ignore -v .DS_Store
.gitignore:1:.DS_Store	.DS_Store

Here is the output when the repository’s .git/info/exclude is ignoring .DS_Store:

$ git check-ignore -v .DS_Store
.git/info/exclude:7:.DS_Store	.DS_Store

Here is the output when the global ~/.config/git/ignore file is ignoring .DS_Store:

$ git check-ignore -v .DS_Store
/Users/nelson/.config/git/ignore:2:.DS_Store	.DS_Store

And here is the output when a custom global ignore file .gitignore_global is ignoring .DS_Store:

$ git check-ignore -v .DS_Store
/Users/nelson/.gitignore_global:1:.DS_Store	.DS_Store

If there is nothing ignoring a file, the git check-ignore -v command produces no output.

This post received a lot of attention on Hacker News! Check it out here: https://news.ycombinator.com/item?id=48583356

To clone a specific branch of a git repository without cloning all other branches, use the following command formula:

git clone --single-branch --branch <branch_name> <repo_URL.git>

For example, if you want to clone the release-1.28 branch of the Kubernetes GitHub repository, run:

git clone --single-branch --branch release-1.28 https://github.com/kubernetes/kubernetes.git

Cloning the Latest Commit of a Specific Branch

If you only want to clone the latest commit of a specific branch (which results in a faster and smaller cloning operation) use --depth 1. The command formula looks like this:

git clone --single-branch --branch <branch_name> --depth 1 <repo_URL.git>

And here is another example using the release-1.28 branch of the Kubernetes GitHub repository:

git clone --single-branch --branch release-1.28 --depth 1 https://github.com/kubernetes/kubernetes.git

References

• https://www.freecodecamp.org/news/git-clone-branch-how-to-clone-a-specific-branch/
• https://git-scm.com/docs/git-clone

With git shortlog you can list all contributor emails for any git repository, not just GitHub repos.

Disclaimer:

I am writing about this to make others aware of this form of scraping and it is purely for educational purposes. I do not plan on doing anything with emails from git repos and you shouldn’t either.

tl;dr:

You can run this command within any git repo to extract all contributor emails:

git shortlog -sea | grep -E -o "\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,6}\b" | awk '{print tolower($0)}' | sort | uniq | grep -wv 'users.noreply.github.com'

Command Break Down

The git shortlog -sea part of the command is short for git shortlog --summary --email --all. This command outputs the number of commits each user has made, along with their name and email, across all branches.

$ git shortlog -sea

    54  First Last <FirstLast@example.com>
   385  Another User <Anotheruser@example.com>
     2  user1 <user1@example.com>
    31  first last <firstlast@example.com>
    10  Someone Else <1234567+someoneelse@users.noreply.github.com>

The next command, grep -E -o "\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,6}\b", extracts emails from each line using a regular expression.

$ git shortlog -sea | grep -E -o "\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,6}\b"

FirstLast@example.com
Anotheruser@example.com
user1@example.com
firstlast@example.com
1234567+someoneelse@users.noreply.github.com

The output from the previous command is piped into awk '{print tolower($0)}', which lowercases all the emails. Sometimes emails are typed in with capital letters. Lowercasing all characters will help with sorting and finding unique emails later.

$ git shortlog -sea | grep -E -o "\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,6}\b" | awk '{print tolower($0)}'

firstlast@example.com
anotheruser@example.com
user1@example.com
firstlast@example.com
1234567+someoneelse@users.noreply.github.com

After that, the output is piped into sort and uniq. These commands are straightforward. The emails are sorted alphabetically, then duplicates are excluded from the output.

$ git shortlog -sea | grep -E -o "\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,6}\b" | awk '{print tolower($0)}' | sort | uniq

1234567+someoneelse@users.noreply.github.com
anotheruser@example.com
firstlast@example.com
user1@example.com

That should suffice for a lot of git repos, but I also added grep -wv 'users.noreply.github.com' to the end of the command to exclude noreply emails associated with GitHub.

$ git shortlog -sea | grep -E -o "\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,6}\b" | awk '{print tolower($0)}' | sort | uniq | grep -wv 'users.noreply.github.com'

anotheruser@example.com
firstlast@example.com
user1@example.com

Extracting Emails With git log

It’s possible to do something similar with the git log --pretty="%ce" command. However, I noticed that this command does not show as many emails as git shortlog. I didn’t look too much into it, but I believe it only pulls emails from one branch rather than all branches like with git shortlog --all.

References

I learned about git shortlog from this Stack Overflow question:

• https://stackoverflow.com/questions/9597410/list-all-developers-on-a-project-in-git

I got the email regex from here:

• https://www.shellhacks.com/regex-find-email-addresses-file-grep/

Note:

Git Emails

When setting up Git on the command line, you are asked for your email. When pushing commits to GitHub, the email you are using for Git gets pushed along with your code as part of the metadata. While your GitHub email does not publicly show when viewing a repository’s commits, it does come up when viewing commits using the GitHub API.

This presents a privacy risk and the potential for someone to find the email associated with your GitHub account. I wanted to see how easily someone could do this so I created a scraper to do this for me. It turns out it’s not hard to scrape commits for emails that are otherwise hidden from public view.

Disclaimer:

I don’t plan on doing anything malicious with this script or the emails collected. I did this out of curiosity and for demonstrational purposes.

The scraper I created is below. Instructions can be found on the README:

• https://github.com/nelsonfigueroa/github-email-scraper

Scraping for Emails

By running the script, I can scrape for emails found in each commit for a given repository:

$ ruby main.rb -u torvalds -r linux

	+-------------------+
	|   GitHub          |
	|       Email       |
	|         Scraper   |
	+-------------------+


Scraping https://github.com/torvalds/linux/
Rate limit exceeded.
Pages scraped: 1-46 out of 10449
53 emails written to torvalds-linux.txt

Just like that, I’ve scraped several emails. It’s not much, and I could get a lot more if I bothered to authenticate to prevent rate limiting. A patient scraper could simply run this periodically to get as many emails as possible.

So what can we do about this?

Hiding your Email in GitHub Commits

You can choose to hide your email when performing Git operations on the GitHub site as well as the command line. There are two checkboxes you’ll need to tick. Instructions are below:

• Blocking command line pushes that expose your personal email address

Next, you’ll need to change your email Git uses on your machine to the @users.noreply.github.com email that GitHub provided in the previous step. Run the following:

$ git config --global user.email "00000000+yourusername@users.noreply.github.com"

Then verify that the email has been set:

$ git config --global user.email
00000000+yourusername@users.noreply.github.com

Now your actual email will be hidden from Git commits that have been pushed from your machine as well as any Git operations on GitHub. Note that your email will still show up in older commits that were pushed before these changes. However, this will still improve your privacy on GitHub going forward.