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Git

Index

Workflow Branching Strategies

This is a big topic which warrants its own page:

Git Workflow Branching Strategies

Advanced Git Config

HariSekhon/DevOps-Bash-tools - .gitconfig

HariSekhon/DevOps-Bash-tools - .gitignore

You can inherit all configs by just cloning the repo and make link to symlink them to your home directory:

git clone https://github.com/HariSekhon/DevOps-Bash-tools bash-tools
cd bash-tools
make link

GitHub SSH Key SSO Authorization

See GitHub page - SSH Key SSO Authorization

Git HTTPS Authentication

Using HTTPS for git clone / pull / push are more likely to bypass egress content filters on wifi portals for those of you who travel a lot such as remote workers and digital nomads.

Credential helper config for this can be added to an individual git repo or at the global level which is shown in the advanced .gitconfig introduced above.

There is a script to add it to your local repo in the DevOps-Bash-tools:

git_remotes_set_https_creds_helpers.sh

After that you need either $GH_TOKEN or $GITHUB_TOKEN (in that order of precedence) in your environment variables.

Create your GitHub Personal Access Token (PAT) here:

https://github.com/settings/tokens

Or you can install Git Credentials Manager which will prompt for your credentials and cache them the first time you git pull over HTTPS.

CLIs

Standard Git CLI is already provided by XCode on Mac but you can also install it from Homebrew to get a different version:

brew install git

GitHub CLI:

brew install gh

You will need to export $GH_TOKEN for the GitHub CLI. Create your token here.

GitHub specific git commands to make things like cloning GitHub repos shorter:

brew install hub

GitLab CLI:

gem install --user-install gitlab

Bitbucket CLI:

pip install --user bitbucket-cli

GitHub Badges

https://github.com/commonality/architecture-decision-records/wiki/GitHub-repository-status-badges

Basic Tips

  • Commit frequently:
    • make small, atomic commits for easier tracking and diffs
  • Push frequently to your remote origin as a backup:
    • in case you have a local disaster
  • Write clear commit messages:
    • summarize what changed and more importantly why
    • some companies prefix Jira ticket numbers to their commits or Pull Requests
      • Jira can be configured to automatically link a field in each ticket to such PRs
  • Use Comments to explain any clever tricks in code:
    • it's better than git blame which may get covered up on subsequent edits
  • Use branches:
  • Keep branches short-lived:
  • Pull and merge to your branch frequently:
    • this minimizes merge conflicts
    • resolve merge conflicts early
      • they will get bigger over time if you don't merge and resolve conflicts reguarly
  • Don't commit large files:
    • it'll slow down your repo cloning and local checkout size
    • use .gitignore to exclude unnecessary files like large or binary files
    • large files are better handled in external blob storage
    • if you really need large files in Git, see Git LFS further down
  • Don't Rebase - read The Evils of Git Rebasing
    • it's not the default for good reason, it causes more problems
  • Use tags for releases:
    • mark important commits like version, stable releases
    • before and after big refactors
  • Use Pull Requests for better tracking
  • Use Branch protections to:
    • ensure your important trunk branches like master / main or environment branches don't get accidentally deleted
    • enforce code peer review approvals on Pull Requests before merging for quality control
    • this is to sanity check design and approach rather than linting for minor typos and errors which CI/CD should catch instead
  • Use CI/CD for extensive linting and testing:
    • set this up asap to trigger on both trunk and especially Pull Requests
      • this can block introducing rubbish code & style
    • you are inheriting technical debt daily until you set this up and will end up with ever more code to fix up the longer you delay adding this

Advanced Tips & Tricks

Git Clone using a specific SSH Key

Git SSH Clone with a specific private key:

GIT_SSH_COMMAND="ssh -i teamcity_github_ssh_key" git clone git@github.com:ORG/REPO

Show files not being tracked due to global & local .gitignore files

git status --ignored

Find line in .gitignore which is causing a given file to be ignored

If you have a large .gitignore and want to find which line is causing a file to be ignored, do this:

git check-ignore -v -- .github/scripts/

output:

/Users/h.sekhon/.gitignore:3711:[Ss]cripts      .github/scripts/

Trigger CI/CD using empty commit

Use for cases where PR checks are failing on PR metadata and you just need a fresh run triggered but don't need to change your branch contents.

This has the advantage of avoiding dismissing your already hard earnt GitHub Pull Request approvals and re-bugging your colleagues to re-approve some trivial unnecessary change.

git commit --allow-empty -m 'Empty commit to trigger CI'

Copy a file from another branch

git checkout "$branch" "$filename"

This puts it straight into the cache for commit, so you'll need to git reset if you don't want to commit it.

Pull from Upstream Origin in a local Fork

To make it easier to stay up to date with an upstream source repo when you're in a clone of its fork, add it:

git remote add upstream "$url_to_original_repo"

You can then pull from the upstream to your local fork branch:

git pull upstream main

Remember not to make any commits to your fork's main trunk branch.

It needs to stay cleanly aligned with the upstream and only be used to merge upstream updates into your personal feature branch in your fork.

That personal feature branch will contain your changes to raise pull requests back to the main trunk branch of the upstream repo.

Multi-Origin Remotes

Store your repo on multiple Git repo providers.

Useful for backups in case there is an outage to GitHub / GitLab / Bitbucket / Azure DevOps - you can still pull / push to the other.

Add one or more remote repo URLs to the current git checkout:

See bash-tools/git/git_remotes_set_multi_origin.sh which automates this to all major Git hosting providers

git remote set-url --add origin $url2
git remote set-url --add origin $url3

See the remotes configured for origin:

$ git remote -v
origin  git@github.com:HariSekhon/DevOps-Bash-tools (fetch)
origin  git@github.com:HariSekhon/DevOps-Bash-tools (push)
origin  git@gitlab.com:HariSekhon/DevOps-Bash-tools (push)
origin  git@bitbucket.org:HariSekhon/DevOps-Bash-tools (push)
origin  git@ssh.dev.azure.com:v3/harisekhon/GitHub/DevOps-Bash-tools (push)

A standard git push will then push to all URLs for upstream hosted repos:

git push

Pull from all remotes:

git pull --all

Fetch all branches from all remotes but does not merge changes in, similar to git fetch but for all branches:

git remote update

Advanced - push to different branch on remote

Configures the remote to push local master branch to dev branch upstream

git config remote.<name>.push master:dev

Fix Author / Email in Git Pull Request or History

If you've accidentally committed using your personal email at work or worse, your work email in your public github projects, I've written a script to make this easy by wrapping git filter-branch.

A force push would be required which will replace all later hash refs after the first change and cause conflicts with existing checkouts which if merged could re-introduce the bit you don't want. You must coordinate with your peers to replace their clones in that case if they're already pulled.

git clone https://github.com/HariSekhon/DevOps-Bash-tools bash-tools
bash-tools/git/git_filter_branch_fix_author.sh --help  # for details

Erase Leaked Credential in Pull Request

GitHub has added automation for support ticket requests to delete a pull request containing a credential.

If you reset the branch contents and force push without the credential then you may not need to even delete the PR as it'll replace the diff.

First remove the credential from the file(s).

Find the common divergence point for your branch:

base_branch="master"  # or main
your_branch="$(git branch --show-current)"
base_commit="$(git merge-base "$base_branch" "$yourbranch")"

git diff --name-only "$base_branch".."$your_branch" >> filelist.txt

Roll back the branch to the fork point:

git reset "$base_commit"

Re-add all the files you add/updated in this branch:

git add $(cat filelist.txt)

Re-commit all the changed files:

git commit -m "squashed all branch changes into one commit to wipe out the credential that shouldn't have been in there")

Then force push to overwrite the Pull Request contents to wipe out the leaked credential:

git push --force

(if you get an error you need to temporarily disable the force push branch protection)

Convert GitHub.com links to Raw GitHub URL links

Raw content path for PNG images.

Sometimes GitHub doesn't give you the raw link for a PNG file that it does for an SVG file, eg. compare these two pages:

SVG has a raw link button:

https://github.com/HariSekhon/Diagrams-as-Code/blob/master/images/kubernetes_traefik_ingress_gke.svg

but PNG doesn't:

https://github.com/HariSekhon/Diagrams-as-Code/blob/master/images/kubernetes_kong_api_gateway_eks.png

Convert the standard GitHub page link to a raw link:

github_link="https://github.com/HariSekhon/Diagrams-as-Code/blob/master/images/kubernetes_kong_api_gateway_eks.png"
echo "$github_link" |
sed 's|https://github.com/|https://raw.githubusercontent.com/|; s|/blob/|/|'

output:

https://raw.githubusercontent.com/HariSekhon/Diagrams-as-Code/master/images/kubernetes_kong_api_gateway_eks.png

Git Filter-Repo

https://github.com/newren/git-filter-repo

3rd party Git command add-on that's useful for replacing a token, author name/email, or excluding files and is recommended over the lower-level git filter-branch.

Git Filter-Repo Analyze

Creates a bunch of text files with interesting stats on the contents of the repo to figure out what to replace:

git filter-repo --analyze

less .git/filter-repo/analysis/*

Git Filter-Repo Replace Text in Commit History

Useful to remove tokens accidentally committed.

It's too late if the commits with the token have been pushed as the upstream repo could have been cloned after push so you can't get it back. If nobody has cloned you can force push to wipe it from the upstream history but you can't guarantee that the repo wasn't pulled/cloned and that the token isn't compromised so it should be rotated and invalidated for safety.

See git_filter_repo_replace_text.sh

Git Filter-Repo Remove File(s) from Commit History

Remove all the paths specified in the text file:

git filter-repo --invert-paths --paths-from-file paths_to_remove.txt  # --force

(git filter-repo --help for details on the path file format)

See git_files_in_history.sh to see what files are in the git history that you might want to remove.

Erase Leaked Credential in Git History

Can also be used to remove reference to client names in public projects.

First clone DevOps-Bash-tools, then run the script in there:

bash-tools/git/git_filter_repo_replace_text.sh --help  # for details

Merge a branch from another repo into the current repo

git fetch "$git_repo_url_or_checkout_directory" +"$remote_branch":"$locally_mirrored_branch"

Merge it into the current branch, eg. main

git merge --allow-unrelated-histories "$locally_mirrored_branch"

Then see the Git Filter-Repo Remove File(s) from Commit History section to remove files from the history of the other repo that you don't want polluting and bloating your new repo.

Reset and Re-download Git Submodule

To resolve submodule update merge conflicts:

  1. Delete the submodule directory
  2. Delete the .git/modules cache of the submodule
rm -fr ".git/modules/$name"
  1. Re-initialize the submodule
git submodule update --init --recursive

Get the Default Branch

git symbolic-ref refs/remotes/origin/HEAD | sed 's|.*/||'

Get Current Branch

git rev-parse --abbrev-ref HEAD

In newer versions of Git version 2.22 (Q2 2019+):

git branch --show-current

Find which upstream <remote>/<branch> the current branch is set to track

git for-each-ref --format='%(upstream:short)' "$(git symbolic-ref -q HEAD)"

List files changed on current branch vs default branch

First find the trunk default branch to compare to the current branch:

default_branch="$(git symbolic-ref refs/remotes/origin/HEAD | sed 's|.*/||')"

Then find the changed files since branching from the trunk default branch:

git diff --name-only "$default_branch"..

or

git log --name-only --pretty="" "origin/$default_branch".. | sort -u

If you forget to the set the default_branch by running the first command you'll get this error:

fatal: ..: '..' is outside repository at '/Users/hari/github/bash-tools'

List files added on current branch vs default branch

default_branch="$(git symbolic-ref refs/remotes/origin/HEAD | sed 's|.*/||')"
git log --diff-filter=A --name-only --pretty="" "origin/$default_branch".. | sort -u

Push New Branch and Set Upstream in One Command

git push --set-upstream origin "$(git rev-parse --abbrev-ref HEAD)"

Push New Branch and Raise Pull Request in One Command

Using DevOps-Bash-tools repo scripts:

On GitHub

Push and open the PR in your web browser to click complete:

github_push_pr_preview.sh

Push and create the PR immediately (see --help description for options including immediately merge):

github_push_pr.sh

On GitLab

Push and open the PR in your web browser to click complete:

gitlab_push_pr_preview.sh

Push and create the PR immediately (see --help description for options including immediately merge):

gitlab_push_pr.sh

If sourcing DevOps-Bash-tools .bashrc then you can simply type:

pushu  # to push and preview the PR

or

pushup  # to push and raise the PR

Git LFS

https://git-lfs.com/

Store big files in GitHub repos (1GB limit for free accounts).

I used this to store old training materials like videos, PDFs, zip files etc. so they are safe and I can then save space locally.

GitHub will block files over 100MB from being git push otherwise.

Install Git LFS extension on Mac:

brew install git-lfs

Install the Git LFS config into your $HOME/.gitconfig:

git lfs install

In your repo add the big file types to be tracked in your local repo (configures .gitattributes):

git lfs track '*.mp4'

Commit the .gitattributes changes:

git add .gitattributes
git commit -m "add mp4 file type to be tracked by Git LFS in .gitattributes"

Override global extensive .gitignore if you've copied it from or installed DevOps-Bash-tools using a local repo .gitignore.

See files being ignored.

echo '!*.mp4' >> .gitignore
git commit -m "allowed .mp4 files to be git committed in .gitignore"
git add *.mp4
git commit -m "added mp4 videos"

Automatically uploads the files to GitHub or whatever is configured as your upstream Git server using LFS storage:

git push

See LFS details:

git lfs env

On another computer you must install Git LFS before you clone.

Otherwise you'll get a checkout with 4K pointer files instead of the actual file contents because Git LFS smudges the checkout to download the file blobs to replace in your checkout.

Why You Need Git LFS for Large Files

You'll get errors like this trying to push large files to GitHub:

$ git push -u origin master
Enumerating objects: 52, done.
Counting objects: 100% (52/52), done.
Delta compression using up to 4 threads
Compressing objects: 100% (52/52), done.
Writing objects: 100% (52/52), 584.76 MiB | 2.05 MiB/s, done.
Total 52 (delta 0), reused 0 (delta 0)
remote: warning: File COURSE.pdf is 69.89 MB; this is larger than GitHub's recommended maximum file size of 50.00 MB
remote: warning: File COURSE2.pdf is 64.61 MB; this is larger than GitHub's recommended maximum file size of 50.00 MB
remote: error: Trace: 98e304dad85b91bcb5f726886ddce1b51a5b450523fc93f44ea51e64b444b69c
remote: error: See https://gh.io/lfs for more information.
remote: error: File COURSE.mp4 is 100.27 MB; this exceeds GitHub's file size limit of 100.00 MB
remote: error: GH001: Large files detected. You may want to try Git Large File Storage - https://git-lfs.github.com.
To github.com:HariSekhon/training-old.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'git@github.com:HariSekhon/training-old.git'

Git LFS on other hosting providers

GitLab works fine for both push and clone.

Azure DevOps seems to work for push but doesn't show the file contents in the web UI preview and cloning resulted in a checkout error after clone and neither git restore --source=HEAD :/ nor git reset HEAD --hard worked to get Git LFS to smudge and download the large files.

Unfortunately GitHub limits large files to only 1GB for free accounts, so only use it for files over 100MB. GitHub will disable your LFS after you go over the thresholds for storage or bandwidth usage for the month.

Bitbucket is useless because the free tier only gives 1GB storage (use GitHub instead):

$ git push bitbucket
Uploading LFS objects:   0% (0/51), 0 B | 0 B/s, done.
batch response:
********************************************************************************
[ERROR] Your LFS push failed because you're out of file storage
[ERROR] Change your plan to get more file storage:
[ERROR] https://bitbucket.org/account/user/harisekhon/plans
********************************************************************************

error: failed to push some refs to 'git@bitbucket.org:HariSekhon/training-old.git'

Bitbucket also requires disabling locking:

git config lfs.https://ssh.dev.azure.com/v3/<user>/<project>/<repo>.git/info/lfs.locksverify false

Multi-origin pushes fail and require individual remote pushes:

$ git push
...
remote: GitLab: LFS objects are missing. Ensure LFS is properly set up or try a manual "git lfs push --all".
To gitlab.com:HariSekhon/training-old.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'git@gitlab.com:HariSekhon/training-old.git'
...

$ git push gitlab

Partial port from private Knowledge Base page 2012+