Understanding git as Version Control System

Git allows you to create versions of your files and therefore it is known as the “Version Control System”. The following table compares others types of systems that allow to create versions and the features they provide:

Versions	Any Editor	Use Offline	Manual Save
Manual	Yes	Yes	Yes
Drop Box	Yes	No	No
Google Doc	No	No	No
Wikipedia	No	No	Yes
Git	Yes	Yes	Yes
SVN	Yes	No	Yes

Fundamental concept

Git system comprises of the local repository and the remote repository. The local repository manages your versions in your local machine and remote repository syncs your work from local to the remote so it be shared with others. The local repository has three virtual areas - 1. working directory, 2. staging area and the 3. commit history. git add command is used to move the files from the working directory to the staging area. git commit takes the snapshot of files in the staging area and adds it to the commit history. It is recommended to make a commit after each logical change in your code. When you are ready to share your code, you run git push command to sync with the remote.

Basic Commands

View the history of all commits of the current branch in a repository

git log

Logs that show the files changed

git log --stat

View the 5 most recent commits of the current branch in a repository

git log -n 5

View the difference between the given two commits

git diff a5c d4e

Compares the given commit to its parent

git show d4e

Get the remote repository to your local. Does two things - 1. creates a local branch called “master” and 2. creates a local branch called “origin/master” which is the last known snapshot of the remote

git clone remote-url

Resets the repository to the given commit

git checkout d4e

Branches

List all branch

git branch

List all branch including the origin/master branch that is automatically created at the time of git clone

git branch -a

Create a branch with the given branch name

git branch <branch_name>

Change the branch to the given branch

git checkout branch_name

View the history of all commits in the given branch. Note: if you want to see the history of commits in a remote repository, then the command to use git log origin/master. More to come on this later, but you should know for now that “origin/master” is the local copy of the remote origin master branch

git log branch_name

View all commits of the given branches - master and coins

git log --graph --oneline master coins

Delete a branch. Deleting a branch makes all commits in the branch unreachable. Git garbage collector will delete the commits later

git branch -d coins

Run Git’s garbage collector manually

git gc

Merge the branch “coins” into “master”

git merge coins master

Deletes a remote branch

git push origin --delete <name of remote branch>

Remotes

Get the name of the remote

git remote

Add a remote to the local repository and give it a name

git remote add origin remote_url

List all remote names including the corresponding remote url added to the local repository

git remote -v

Merges the local commits to the remote named “origin” to “master” branch

git push origin master

Merges the master branch of the remote to the master branch of the local

git pull origin master

GitHub Jargons

Conflicting Collaboration

If there are different changes in the local and remote, extra work needs to be done to resolve the conflict. Usually, it is a two-step process - git fetch origin Merges the remote’s master branch to the local origin/master git merge master origin/master Merges the local master branch to the local origin/master

In fact, git pull origin master runs the exact above two commands. You can use git status to see the status of your local before and after the fetch. Before the fetch, the command will show that your branch is ahead of origin/master by certain number of commits. After the fetch, the git status command will show that your branch and the origin/master have diverged. After successful merge (the second step), the git status command will show that your branch is up-to-date with the origin/master.

Concept of fast-forward merge

If there is no conflicting change between the remote and the local, git pull command will merge the remote with the local branch by moving the label from an older commit to the most recent commit. This type of merge is called a fast-forward merge. In this type of merge, the branch to merge is the parent of the branch to merge into.

Configuration

Cache git password

git config --global credential.helper cache

Set default editor for commit messages

git config --global core.editor "vim"

Set push default

git config --global push.default matching

Set diff format

git config --global merge.conflictstyle diff3

The above commands create a .gitconfig file in the home directory.

Advanced commands

Cherry pick all commits from a merge commit of a branch into a branch

git checkout release-branch
git cherry-pick -m 1 merge-commit-hash
git push origin release-branch

Cherry-picking certain commits into a branch

git checkout release-branch
git cherry-pick xyzabc123
git push origin release-branch

Undoing change from a merged PR from a branch

# Checkout the branch where the PR was merged and run the following command
git revert -m 1 commit_id_of_merge_pr

git revert makes new commits to remove old commits in a way while keeping the commit history. This is the recommended way to undo a commit. There is also another command called git reset , but this doesn’t keep the history of your commits.

Undoing change to a particular commit

git revert --no-commit commit_sha..HEAD

Push reference of one branch to another

git push origin master:production

List commit logs with reference

git reflog

• Miscellaneous