Advance Git & GitHub for DevOps Engineers

1. What is Git Branching?

• Git branching is a feature in Git that allows you to diverge from the main line of development and continue to do work without messing up that main line.

• Git branching is like creating a copy of your project to work on without affecting the original.

• Branching means you can create a copy of your project to work on a specific feature, fix a bug, or experiment with new ideas without affecting the main project.

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2. What is Git Revert and Reset?

Git Revert

• "Git revert" is used to undo the changes introduced by a specific commit by creating a new commit with the opposite changes. This method maintains the project history intact, making it clear what was changed and why it was reverted.

• Use case: When you want to undo changes in a way that preserves the history of the repository.

linux$ git revert <commit-hash>

Git reset

• "Git reset" is used to undo changes by moving the current branch pointer to a different commit.

• Moves the branch pointer back to a previous commit, effectively discarding any commits made after that point.

• Rewrites the commit history, which can be risky if others have already pulled your code.

There are three types of reset,

• Soft Reset (--soft): Moves the branch pointer to a different commit but leaves your working directory and the index (staging area) unchanged.

linux$ git reset --soft <commit-hash>

• Mixed Reset (--mixed): Moves the branch pointer to a different commit and resets the index, but leaves your working directory unchanged.

linux$ git reset --mixed <commit-hash>

• Hard Reset (--hard): Moves the branch pointer to a different commit and resets both the index and working directory to match that commit.

linux$ git reset --hard <commit-hash>

For a better understanding of Git Rebase and Merge, check out this article.

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3. What is Git Rebase and Merge?

Git Merge

• "Git merge" combines changes from one branch into another. It creates a new commit, called a "merge commit," which has two parent commits.

• Suppose you want to merge two branch then first go to the main base branch and then try to merge branch that you want to merge, for e.g,

linux$ git checkout master # Switched to master branch
linux$ git merge feature-branch # Trying to merge branch feature-branch to main

Git Rebase

• "Git rebase" moves or combines a sequence of commits to a new base commit. Instead of creating a merge commit, rebase rewrites the project history by creating new commits for each commit in the original branch.

• When you want to incorporate changes from one branch into another without creating a merge commit, resulting in a cleaner project history.

linux$ git checkout feature-branch
linux$ git rebase master

For a better understanding of Git Rebase and Merge, check out this article.

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4. Task 1 : Feature Development with Branches

Create a Branch and Add a Feature

• Add a text file called version01.txt inside the Devops/Git/ directory with “This is the first feature of our application” written inside.

linux/Devops/Git/Adv_git$ ls
version01.txt
linux/Devops/Git/Adv_git$ cat version01.txt
This is the first feature of our application.

• Create a new branch from "master".

linux/Devops/Git/Adv_git$ git branch dev
linux/Devops/Git/Adv_git$ git branch
  dev
* master

• Commit your changes with a message reflecting the added feature.

linux$ git checkout dev
D       README.md
Switched to branch 'dev'

linux$ git add version01.txt
linux$ git commit -m "Added new feature"

Push Changes to GitHub

• Push your local commits to the repository on GitHub.

/linux/Devops/Git/Adv_git$ git status
On branch dev
nothing to commit, working tree clean

linux/Devops/Git/Adv_git$ git push origin dev
Enumerating objects: 4, done.
Counting objects: 100% (4/4), done.
Writing objects: 100% (3/3), 300 bytes | 150.00 KiB/s, done.
Total 3 (delta 0), reused 0 (delta 0)
remote:
remote: Create a pull request for 'dev' on GitHub by visiting:
remote:      https://github.com/ojasjawale/Adv_git/pull/new/dev
remote:
To github.com:ojasjawale/Adv_git.git
 * [new branch]      dev -> dev

Add More Features with Separate Commits

• Update version01.txt with the following lines, committing after each change.

• 1st line: This is the bug fix in development branch

linux/Devops/Git/Adv_git$ git commit -am "Added feature2 in development branch"
[dev 4cf98e2] Added feature2 in development branch
 1 file changed, 2 insertions(+)

linux/Devops/Git/Adv_git$ git log --oneline
4cf98e2 (HEAD -> dev) Added feature2 in development branch
63c03df (origin/dev) Added new feature
9f59996 (origin/master, origin/HEAD, master) Initial commit

• 2nd line: This is Gadbad code.

linux/Devops/Git/Adv_git$ echo "This is gadbad code" >> version01.txt

linux/Devops/Git/Adv_git$ git commit -am "Added feature3 in development branch"
[dev 04600e2] Added feature3 in development branch
 1 file changed, 2 insertions(+)

linux/Devops/Git/Adv_git$ git log --oneline
04600e2 (HEAD -> dev) Added feature3 in development branch
4cf98e2 Added feature2 in development branch
63c03df (origin/dev) Added new feature
9f59996 (origin/master, origin/HEAD, master) Initial commit

• 3rd line: This feature will Gadbad everything from now.

linux/Devops/Git/Adv_git$ echo "This feature will gadbad everything from now" >> version01.txt       

linux/Devops/Git/Adv_git$ git commit -am "Added feature4 in development branch"
[dev 5dc8e94] Added feature4 in development branch
 1 file changed, 1 insertion(+)

linux/Devops/Git/Adv_git$ git log --oneline
5dc8e94 (HEAD -> dev) Added feature4 in development branch
04600e2 Added feature3 in development branch
4cf98e2 Added feature2 in development branch
63c03df (origin/dev) Added new feature
9f59996 (origin/master, origin/HEAD, master) Initial commit

Restore the File to a Previous Version

• Revert or reset the file to where the content should be “This is the bug fix in development branch”.

linux/Devops/Git/Adv_git$ cat version01.txt
This is the first feature of our application.

This is the bug fix in development branch
This is gadbad code
This feature will gadbad everything from now

linux$ git revert HEAD~2

linux/Devops/Git/Adv_git$ cat version01.txt
This is the bug fix in development branch

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5. Task 2 : Working with Branches

Demonstrate Branches

• Create 2 or more branches and take screenshots to show the branch structure.

linux$ git branch stg
linux$ git branch prd
linux$ git branch
* dev
  master
  prd
  stg

Merge Changes into Master

• Make some changes to the dev branch and merge it into master.

linux/Devops/Git/Adv_git$ git checkout master
Switched to branch 'master'
Your branch is up to date with 'origin/master'.

linux/Devops/Git/Adv_git$ git merge dev
Updating 9f59996..6f3f6fe
Fast-forward
 README.md     | 1 -
 version01.txt | 1 +
 2 files changed, 1 insertion(+), 1 deletion(-)
 delete mode 100644 README.md
 create mode 100644 version01.txt

Practice Rebase

• Try rebasing and observe the differences.

linux/Devops/Git/Adv_git$ git rebase master
Current branch master is up to date.

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