Tutorial: GIT and GitHubCreating & switching Branches - 2020

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Head & Master

Here is the initial file structure for heads under .git directory:

Currently, the HEAD is at master branch which is the default branch (.git/refs/heads/master). Actually, the heads directory contains all the heads and we see our master branch is right there.

Creating Branches

Let's create a new branch called 'car':

k@laptop:~/GitDemo$ git branch car
k@laptop:~/GitDemo$ git branch
  car
* master

Now we have two branches and the (*) indicates the HEAD is pointing to the master branch. If we look at the directory structure again:

Now we have two heads for our branches ('car' and 'master').

Switching Branches

Switching to another branch is simple: use git checkout branch_name:

k@laptop:~/GitDemo$ git branch
  car
* master

k@laptop:~/GitDemo$ git checkout car
Switched to branch 'car'

k@laptop:~/GitDemo$ git branch
* car
  master

Now we are on 'car' branch.

But each of our two branches points to the same thing:

k@laptop:~/GitDemo$ git branch
* car
  master
k@laptop:~/GitDemo$ ls
Appendix  Book1  Introduction

k@laptop:~/GitDemo$ git checkout master
Switched to branch 'master'

k@laptop:~/GitDemo$ git branch
  car
* master
k@laptop:~/GitDemo$ ls
Appendix  Book1  Introduction

Let's modify the 'Book1' in t he'car' branch.

So, the first line of the 'Book1' looks like this:

This is in 'car' branch.

Then, we do commit:

k@laptop:~/GitDemo$ git status
On branch car
Changes not staged for commit:
  (use "git add ..." to update what will be committed)
  (use "git checkout -- ..." to discard changes in working directory)

	modified:   Book1

no changes added to commit (use "git add" and/or "git commit -a")
k@laptop:~/GitDemo$ 
k@laptop:~/GitDemo$ git add Book1
k@laptop:~/GitDemo$ git commit -m "added a line at the beginning"
[car a7f55e3] added a line at the beginning
 1 file changed, 2 insertions(+)

Then, check the log:

k@laptop:~/GitDemo$ git log --oneline
a7f55e3 added a line at the beginning
0c97f22 removed three updates
42dacd8 name changed
...
28a0a9e deleted OldBook
09a5016 Adding OldBook
b440952 initial commit

Note that this log for 'car' branch not for 'master' branch. To see it, we can switch back to 'master' and check the log:

k@laptop:~/GitDemo$ git checkout master
Switched to branch 'master'

k@laptop:~/GitDemo$ git branch
  car
* master

k@laptop:~/GitDemo$ git log --oneline
0c97f22 removed three updates
42dacd8 name changed
...
28a0a9e deleted OldBook
09a5016 Adding OldBook
b440952 initial commit

As we can see the commit we've made is not in this 'master' branch.

Creating & Switching Branches at one shot

Now we want to create a new branch and switch to the new branch at the same time with one git command. We can use -b flag:

k@laptop:~/GitDemo$ git branch
  car
* master
k@laptop:~/GitDemo$ git checkout -b boat
Switched to a new branch 'boat'
k@laptop:~/GitDemo$ git branch
* boat
  car
  master
k@laptop:~/GitDemo$

Another useful option for git log to see where the HEAD is and what's the relationships among branches: