Skip to content

Software Engineering / Tools / Git Source Control Management (SCM)

Git is a source control management tool that helps to keep track of changes made to a codebase.

This page provides an overview of some useful concepts and commands.

Installation

Installation on Ubuntu 16.04

sudo add-apt-repository ppa:git-core/ppa;
sudo apt-get update;
sudo apt-get install git;

Git Branching Models

GitFlow

GitFlow is a branching model for Git created by Vincent Driessen.

  • Generally seen in more traditional enterprise software development where process and stability is prioritised over agility (think Waterfall)
  • 5 types of branches:
  • master branch
  • hotfix branch
  • release branch
  • develop branch

  • feature branch

  • https://datasift.github.io/gitflow/IntroducingGitFlow.html

Trunk-Based Development

Trunk-Based Development is a branching model where developers commit and push to the master branch continuously.

  • Generally seen in more modern software development teams where process and stability is deprioritised over business agility (think Agile)
  • Typically seen with Continuous Delivery (CD) pipelines
  • Usually requires the following to successfully implement/reap full benefits:
  • Agile Software Development Lifecycle (SDLC)
  • Service-oriented architectures (SOA)
  • Observability instrumentation

  • Feature toggling

  • https://trunkbaseddevelopment.com/

Initialisation

Clone a repository

Why

  • I would like to make a local copy of code from a public repository I found online.
# for http-based
git clone https://zephinzer@github.com/zephinzer/blog.joeir.net

# for ssh-based
git clone ssh://git@github.com/zephinzer/blog.joeir.net

Create a new repository

Why

  • I would like to initialise a new Git repository on my computer.
git init

Remote management

Add a Git remote

Why

  • I would like to add a new remote named origin to my repository.
git remote add origin ssh://git@github.com/zephinzer/blog.joeir.net

Update the Git remote

Why

  • I would like to update the URL for my remote named origin in my repository.
git remote set-url origin ssh://git@github.com/zephinzer/blog.joeir.net

Retrieving changes

Fetch changes

Fetching retrieves the changes but does not merge the changes with your local copy.

Why

I would like to get updates from the remote but I don't want to update my code yet.

git fetch

Merge changes

Merging takes the remote changes that have been fetched from the remote and merges them with your local copy.

Why

I have reviewed the changes I retrieved from the remote and I want to update my local code to match the remote's copy now.

git merge HEAD

Pull changes

Pulling basically does a fetch and merge.

Why

I would like to update my code so that it is the same as the remote's.

git pull

Pull with Rebase

Pulling with rebase does a fetch, but before merging in the remote changes, it rolls back to a state before all remote changes were made, applies the remote changes, and then applies your local changes.

Why

I would like to update my code by placing whatever's from the remote before my current changes so that it is the same as the remote's and I don't have a merge commit.

git pull -r

Rebase

Why

  • I would like to pull in changes from another branch that's available locally and place those changes before the changes I've committed.
# assuming we are on branch feature_x pulling in updates from master
git rebase master

Saving changes

Stashing

Why

  • I would like to temporarily store my unstaged changes so that I can pull in the latest updates from the remote.
# put all unstaged changes into a stash
git stash

# checking stashed changes
git stash list

# popping the last stashed change
git stash pop

Staging

Why

  • I would like to add file(s) that will be 'saved' during a commit.
# to stage all changes, run this from project root
git add .

# to stage only one file
git add ./path/to/changed_file

Commiting

Why

  • I would like to save my changes to my local Git repository.
git commit -m 'some message'

Commiting without any changes

Why

  • I would like to add a commit to my local repository without adding any files
  • I would like to have a commit that can trigger a pipeline in the remote source control
git commit --allow-empty 'some message'

Modifying changes

Adding a file to a previous commit

Why

  • I forgot to run git add on a file that should be in the previous commit.
# stage the missing file first
git add ./path/to/missed/file;

# this will add the staged file to the previous commit
git commit --amend

Squash commit

Why

  • I have made 5 commits and I would like to compress them into a single commit so my Git history is cleaner.
# indicate `p` or `pick` for the head commit, and `s` or `squash` for the rest
git rebase -i HEAD~5

Squashing till origin/master/HEAD

Why

  • I have made X number of commits to my branch and want to squash/rebase my commits within my branch so that a rebase with master will be cleaner
git rebase -i HEAD~$(git log --oneline master..HEAD | wc -l);

Uncommit last commit

Why

  • I would like to reverse the last commit but leave changes I made intact
# this will leave the committed files as staged
git reset --soft HEAD^

# this will also unstage all changes
git reset HEAD^

Reverting a commit

Why

  • I would like to create a commit that reverses the changes in a certain commit with hash ${COMMIT_HASH}
# use `git log` to find the commit hash of the commit you wish to undo the effects of
git revert ${COMMIT_HASH}

Submitting changes

Pushing

Why

  • I would like push all committed changes from my computer to the remote
git push

Force Pushing

Why

  • I have modified a commit locally and am unable to push normally to the remote since I rewrote history (WARNING: this will erase any changes others may have made between when the original commit was made, and your current commits)
git push -f

Assessing changes

View all current changes

Why

  • I would like to see what files have been staged
git status

View commit history

Why

  • I want to do an interactive rebase (squashing) and I would like to see which commit I should rebase up till
  • I want to see what changes have been made by other team members/developers
# interactive browsing of git commits
git log

# output only the last 5 logs
git log -n 5

View difference between commits

Why

  • I would like to check out what changes have been made between two commits
# view file changes from HEAD to ${COMMIT_HASH}
git diff HEAD ${COMMIT_HASH}

Viewing repository information

View the Git configuration

Why

  • I would like to see who am I committing code as
git config -l

Check which branch you're on

Why

  • I would like to confirm which branch I am on
git branch

See all remotes

Why

  • I would like to see which remotes I am pushing to
git remote -v

Checking which .gitignore is ignoring a file

Why

  • I would like to know which .gitignore is causing a file to be ignored without any obvious reason
cd `./path/to`;
git check-ignore -v *;

Repository adminstration

Creating a new branch from an existing one

Why

  • I would like to create a new branch based on the current one I'm on
git checkout $SOURCE_BRANCH_SLUG;
git checkout -b $NEW_BRANCH_SLUG;

Deleting a local branch

git branch -D $BRANCH_SLUG;

Deleting a remote branch

git push origin --delete $BRANCH_SLUG;

Deleting local remote branches that have been deleted remotely

git remote update origin --prune;