GIT Commands reference for DevOps Engineer

Dear DevOps Engineer!! this post is full of experimenting with git commands running most of them on the 'Git Bash' window in my laptop. I've collected three things about each git command.

• git command syntax
• What this git command will do - short descriptions
• An example command that I've executed
• Screenshot of that command execution

How do I Start a Fresh repository in Git CLI(local repo)?

You need to create a folder where you would like to start your coding project. The code can be web-site related where you can have multiple directories involved such as HTML files into a folder, all images to be used in the website in a folder, CSS files into a folder, etc. First, make the folder structure for you project then at the root of the project need to initialize the project.  To create empty repo or re-initializing a repo

Syntax :

git init

Note: It is always better to have a fresh directory created and then run the above command to initialize a local Git repository.

git init example

Getting a remote repository to your git client - Local system/Laptop

You can have the remote repository either public or private teams on the following SCM clouds:

1. GitHub 
2. GitLab
3. BitBucket

git clone Syntax:

git clone ssh://git@github.com/[username]/[repository-name].git

Create a local copy of a remote repository of GitHub or Gitlab. Make sure that you're doing first time in that folder, it should not have the same repo that means if your re-run the same command it cannot work.

Please make sure you have the correct access rights and the remote repository exists

Example of using gitlab URL:

 git clone https://github.com/BhavaniShekhar/vtdevops2021feb.git

Vybhava : git clone 

Syntax:

git commit -m "[commit message]"

commit changes
Example:

git commit -m "some message"

git commit command

Syntax:

git checkout -b [branch name origin/[branch name]

Clone a remote branch and switch to it
Example:

git checkout -b feature2

Differences between git checkout & switch command

Syntax:

git checkout [branch name]

Switch to a branch
Example:

git checkout

git checkout command

Syntax :

git checkout -

Switch to the branch last checked out
Example :

git checkout -

git last checkout command

Syntax:

git checkout -- [file-name.txt]

Discard changes to a file on which you are worked recently.
Example:

Syntax:

git push origin [branch name]

push to a branch to your remote repository
 Example:

git push origin slave

git push command

Syntax:

git push -u origin [branch name]

push changes to remote repository (and remember the branch)
Example:

git push -u origin feature1

git push origin command

Syntax:

git push

push changes to remote repository (remembered branch)
Example:

git push

git push command 

Syntax:

git push origin --delete [branch name]

delete a remote branch
 Example:

git push origin --delete feature3

git remote branch delete oush command

git pull command

Syntax:

git pull origin [branch name]

update local repository to the newest commit
Example:

git pull

git pull command

pull changes from remote repository Example:

git pull origin newbranch2

git remote

Syntax:

git remote add origin ssh://git@github.com/[username]/[repository-name].git
    or
 git remote set-url origin ssh://git@github.com/[username]/[repository-name].git

add a remote repository Example 1:

git remote add origin git@gitlab.com:gitops4/docker-exercises.git

set a repository's origin branch to ssh Example 2:

git remote set-url origin git@gitlab.com:gitops4/docker-exercises.git

git log

The syntax for the git log command is:

git log [--summary] [--oneline]

view changes
Example:

git log

git log command

view changes made to files or directory in (detailed)
Example:

    git log --summary

git log summary command

view changes(briefly)
Example:

    git log --oneline

git log oneline command

Syntax:

git diff [source branch] [target branch]

preview changes before merging 

References: 

 Git log command examples https://www.thegeekstuff.com/2014/04/git-log/

Learn how to use git tag for Code Revisions

In this post, let's do an experiment with git tag command options. In GitOps we need to know what is a tag? How many types of git tags? We will learn about Creating, deleting, and listing tags for a project repository. Once everything is done, we need to know how to push the tag to the remote repository.

Work tree for git tag creation

Why git tagging?

1. Tagging is used to mark a commit stage as important
2. We can tag a commit for future references 
3. Typically tagging wiil be used to book mark release points in a Project.
4. Annotated tags will be recommend where you are working in team and collaborating for a project development.

Before you start on git tag

You must have a GitHub or GitLab account to work on a remote repository. Knowledge of basic repository creation on these Git clouds. On your git client shell (git bash as well) you must create the global user identity entries in the configurations.

[vagrant@mydev tags_handson]$ git config --list
user.email=bhavanishekhar@gmail.com
user.name=Pavan Devarakonda
core.repositoryformatversion=0
core.filemode=true
core.bare=false
core.logallrefupdates=true

# Now let's begin
 mkdir tags_handson
 cd tags_handson/
 git init
 echo "test1"> test1.txt

Enter some text into the test1.txt file.

What is git tag?

Git Tags are a simple aspect of the Git version control system, they allow you to identify specific release versions of your application code. You can think of a tag as a branch that doesn't change. Once the git tag is created, it loses the ability to change the history of commits.

Git supports two types of tags:

1. Annotated Tags: Annotated tags, however, are stored as full objects in the Git database.
2. Lightweight Tags: A lightweight tag is very much like a branch that doesn’t change — it's just a pointer to a specific commit.

How to Create tags in Git?

 To create a new tag execute the following command

Annotated tags store extra metadata such as Author name, Release notes, tag-message, and Date as full objects in the Git database. All this data is important for the public release of your project.

Tags can also include a more descriptive tag-message or annotation much like a commit message when you are about to merge. Usually, this is achieved by using (-a for annotation):

git tag -a v1.1 -m 'annotated tag test'

Lightweight tagging

It is simple to create and use, just need to pass the tag name example here for v1.0 the command:

git tag v1.0

How to delete the tags from the local and remote repo?

Unwanted tags we can remove from the repo using the -d or --delete option along with the git tag command. There are two levels of deletion could happens at local and remote

i. Delete a local tag

To remove both types of annotated and lightweight tag use the following git tag command with -d

git tag -d tag_name 

Example:

git tag -d v1.0

Note: If you try to delete a non existig Git tag, there will be the following error: 

git tag -d tag_name error: tag 'tag_name' not found. 

ii. Delete remote tags

To delete a tag from the remote git server with push tags

git push --delete origin remote_tag_name

Hope you are already global configuratoin with remote git server.

Example:

git push --delete origin v1.0.0-rc1

Listing tags 

To list-out all the tags in a work area, we can use

git tag 

Listing git tags
git tag -l '*rc*'

Now in this we can use regular expression in single quotes to see particular tags only, here I've selected all the tags with word contians 'rc'

Listing particular git tags

If you want to list all the tags in sorted order, that based on date :

git log --tags --simplify-by-decoration --pretty="%ai %d"

How to push tags? 

To push a single tag or a specific tag to remote repo:

git push origin v1.0 

To push all tag use following command:

git push origin --tags 

or
To push all the tags to remote (not recommended):

git push --tags 

Run this to push mytag to a project that is hosted on GitHub or GitLab on git origin

git push origin refs/tags/mytag

Best practice using the refs/tags instead of just specifying the . Why? It's recommended to use refs/tags since sometimes tags can have the same name as your branches and a simple git push will push the branch instead of the tag
To push annotated tags and current history chain tags use:

git push --follow-tags

This flag --follow-tags pushes both commits and only tags that are both:
Annotated tags (so you can skip local/temp build tags) Reachable tags (an ancestor) from the current branch (located on the history) 

You should only push annotated tags to the remote repo, and keep lightweight tags for local repo for development to avoid tag clashes. it won't push annotated tags on unrelated branches

Now...

In order to checkout a git tag , you would execute the following command
git checkout tags/tag-name -b branch-name eg as mentioned below.

 git checkout tags/v1.0 -b v1.0-branch 

To fetch the all tags use the command with git fetch:

git fetch --all --tags 

git tag cheat sheet

In my understanding about git tag is like branch but cannot move.

References: 

1. git cheat sheets
2. Stack overflow popular discussion about git tags
3. How do you push tags to Remote Repo