DevOps Classroom Series – 15/Dec/2019 – Git Branching

Merge

• Merge is done when changes from one branch has to be brought to other branches.

• Merges can be of two kinds

  • Fast-Forward:

    • No Extra commit gets created
    • When the Parent branch has no changes and if we try merging child to parent branch
    • Can be skipped

  • Merge:

    • Extra Commit with two parents will be created
    • In all the other cases apart from Fast Forward

• Lets continue from previous repository created from here

• Merge the changes from sprint-1 to master.

• Note that there were no changes in master branch after sprint-1 branch was created, now merging will lead to fast forward

• Lets merge

# move to the destination branch (master)
git checkout master
git merge sprint-1

• Create a branch called as sprint-2 from master

git checkout -b sprint-2

• An Important fix from sprint-1 is done on master.

git checkout master
echo "Updated Docs of Sprint1" >> Readme.md
git status
git add .
git commit -m "added imp fix"

• Continue working on sprint-2 branch

git checkout sprint-2
echo "sprint-2" >> src/main.py
echo "sprint-2" >> test/main.py
git status
git add .
git commit -m "features in sprint 2"

• Now try to merge the changes from sprint-2 to master

git checkout master
git merge sprint-2

• New commit gets created and HEAD & Master will be pointing to this new commit.

• Create a new branch called as sprint-3.

git checkout master
git branch sprint-3
git checkout sprint-3

Rebase

• Now add some changes for sprint-3 branch
• Now an important bug fix is done on master, which is required for sprint-3
• Now to rebase from master onto sprint-3, execute the following commands

git checkout sprint-3
git rebase master

• References:
  • Rebase
  • Merge vs Rebase

Merge-Conflict

• Merge Conflicts can happen during

  • merge
  • rebase
  • pull

• Lets create a child branch from master and call it as poc-qt

git checkout master
git checkout -b poc-qt

• Now add the following to src/main.py at the end

working for qt

• Now master branch has one commit which changes in src/main.py.
• In master branch main.py has the following contents

Sprint 1 Started
SPrint-2
testing is in progress
need to add many comments

• In qt-poc branch main.py has the following contents

Sprint 1 Started
SPrint-2
working for qt

• Conflicts has to be resolved manually.

Viewing Differences

• To view differences, use git diff
• Try the following commands

# make local changes on Working tree
git diff

git diff <commit-id-A> <commit-id-B>

git diff <branch-A> <branch-B>

How is git Working

• Git is internally a very simple content tracker
• To understand this, lets create a new folder called as understanding-git

mkdir understanding-git
cd understanding-git
git init

• Now lets get into .git folder and see the contents
• lets make our first change

mkdir src
touch src/main.py
git add .
git commit -m "Commit-1"
git log

• Now lets make other change

mkdir test
touch test/main.py
git add .
git commit -m "Commit-2"
git log

• To understand how git works , we need to understanding Hashing SHA1
• Git Uses hashing (SHA-1) to calculate commit ids. Commit id is hash of many things.
• To understand contents of commit

git cat-file -p <commit-id>

• Lets examine commit-2 contents
• Take a look at below image