Branching in Git is one of its many great features. If you have used other version control systems, it's probably helpful to forget most of what you think about branches - in fact, it may be more helpful to think of them practically as contexts since that is how you will most often be using them. When you checkout different branches, you change contexts that you are working in and you can quickly context-switch back and forth between several different branches.

In a nutshell you can create a branch with git branch (branchname), switch into that context with git checkout (branchname), record commit snapshots while in that context, then can switch back and forth easily. When you switch branches, Git replaces your working directory with the snapshot of the latest commit on that branch so you don't have to have multiple directories for multiple branches. You merge branches together with git merge. You can easily merge multiple times from the same branch over time, or alternately you can choose to delete a branch immediately after merging it.

The git branch command is a general branch management tool for Git and can do several different things. We'll cover the basic ones that you'll use most - listing branches, creating branches and deleting branches. We will also cover basic git checkout here which switches you between your branches.

git branch list your available branches

Without arguments, git branch will list out the local branches that you have. The branch that you are currently working on will have a star next to it and if you have coloring turned on, will show the current branch in green.

$ git branch
* master

This means that we have a 'master' branch and we are currently on it. When you run git init it will automatically create a 'master' branch for you by default, however there is nothing special about the name - you don't actually have to have a 'master' branch but since it's the default that is created, most projects do.

git branch (branchname) create a new branch

So let's start by creating a new branch and switching to it. You can do that by running git branch (branchname).

$ git branch testing
$ git branch
* master
  testing

Now we can see that we have a new branch. When you create a branch this way it creates the branch at your last commit so if you record some commits at this point and then switch to 'testing', it will revert your working directory context back to when you created the branch in the first place - you can think of it like a bookmark for where you currently are. Let's see this in action - we use git checkout (branch) to switch the branch we're currently on.

$ ls
README   hello.rb
$ echo 'test content' > test.txt
$ echo 'more content' > more.txt
$ git add *.txt
$ git commit -m 'added two files'
[master 8bd6d8b] added two files
 2 files changed, 2 insertions(+), 0 deletions(-)
 create mode 100644 more.txt
 create mode 100644 test.txt
$ ls
README   hello.rb more.txt test.txt
$ git checkout testing
Switched to branch 'testing'
$ ls
README   hello.rb

So now we can see that when we switch to the 'testing' branch, our new files were removed. We could switch back to the 'master' branch and see them re-appear.

$ ls
README   hello.rb
$ git checkout master
Switched to branch 'master'
$ ls
README   hello.rb more.txt test.txt

git branch -v see the last commit on each branch

If we want to see last commits on each branch we can run git branch -v to see them.

$ git branch -v
* master      54b417d fix javascript issue
  development 74c111d modify component.json file
  testing     62a557a update test scripts

git checkout -b (branchname) create and immediately switch to a branch

In most cases you will be wanting to switch to the branch immediately, so you can do work in it and then merging into a branch that only contains stable work (such as 'master') at a later point when the work in your new context branch is stable. You can do this pretty easily with git branch newbranch; git checkout newbranch, but Git gives you a shortcut for this: git checkout -b newbranch.

$ git branch
* master
$ ls
README   hello.rb more.txt test.txt
$ git checkout -b removals
Switched to a new branch 'removals'
$ git rm more.txt 
rm 'more.txt'
$ git rm test.txt 
rm 'test.txt'
$ ls
README   hello.rb
$ git commit -am 'removed useless files'
[removals 8f7c949] removed useless files
 2 files changed, 0 insertions(+), 2 deletions(-)
 delete mode 100644 more.txt
 delete mode 100644 test.txt
$ git checkout master
Switched to branch 'master'
$ ls
README   hello.rb more.txt test.txt

You can see there how we created a branch, removed some of our files while in the context of that branch, then switched back to our main branch and we see the files return. Branching safely isolates work that we do into contexts we can switch between.

If you start on work it is very useful to always start it in a branch (because it's fast and easy to do) and then merge it in and delete the branch when you're done. That way if what you're working on doesn't work out you can easily discard it and if you're forced to switch back to a more stable context your work in progress is easy to put aside and then come back to.

git branch -d (branchname) delete a branch

If we want to delete a branch (such as the 'testing' branch in the previous example, since there is no unique work on it), we can run git branch -d (branch) to remove it.

$ git branch
* master
  testing
$ git branch -d testing
Deleted branch testing (was 78b2670).
$ git branch
* master

git push (remote-name) :(branchname) delete a remote branch

When you're done with a remote branch, whether it's been merged into the remote master or you want to abandon it and sweep it under the rug, you'll issue a git push command with a specially placed colon symbol to remove that branch.

$ git push origin :tidy-cutlery
To git@github.com:octocat/Spoon-Knife.git
 - [deleted]         tidy-cutlery

In the above example you've deleted the "tidy-cutlery" branch of the "origin" remote. A way to remember this is to think of the git push remote-name local-branch:remote-branch syntax. This states that you want to push your local branch to match that of the remote. When you remove the local-branch portion you're now matching nothing to the remote, effectively telling the remote branch to become nothing.

Alternatively, you can run git push remote-name --delete branchname which is a wrapper for the colon refspec (a source:destination pair) of deleting a remote branch.

In a nutshell you use git branch to list your current branches, create new branches and delete unnecessary or already merged branches.

Once you have work isolated in a branch, you will eventually want to incorporate it into your main branch. You can merge any branch into your current branch with the git merge command. Let's take as a simple example the 'removals' branch from above. If we create a branch and remove files in it and commit our removals to that branch, it is isolated from our main ('master', in this case) branch. To include those deletions in your 'master' branch, you can just merge in the 'removals' branch.

$ git branch
* master
  removals
$ ls
README   hello.rb more.txt test.txt
$ git merge removals
Updating 8bd6d8b..8f7c949
Fast-forward
 more.txt |    1 -
 test.txt |    1 -
 2 files changed, 0 insertions(+), 2 deletions(-)
 delete mode 100644 more.txt
 delete mode 100644 test.txt
$ ls
README   hello.rb

more complex merges

Of course, this doesn't just work for simple file additions and deletions. Git will merge file modifications as well - in fact, it's very good at it. For example, let's see what happens when we edit a file in one branch and in another branch we rename it and then edit it and then merge these branches together. Chaos, you say? Let's see.

$ git branch
* master
$ cat hello.rb 
class HelloWorld
  def self.hello
    puts "Hello World"
  end
end

HelloWorld.hello

So first we're going to create a new branch named 'change_class' and switch to it so your class renaming changes are isolated. We're going to change each instance of 'HelloWorld' to 'HiWorld'.

$ git checkout -b change_class
Switched to a new branch 'change_class'
$ vim hello.rb 
$ head -1 hello.rb 
class HiWorld
$ git commit -am 'changed the class name'
[change_class 3467b0a] changed the class name
 1 files changed, 2 insertions(+), 4 deletions(-)

So now we've committed the class renaming changes to the 'change_class' branch. To switch back to the 'master' branch the class name will revert to what it was before we switched branches. Here we can change something different (in this case the printed output) and at the same time rename the file from hello.rb to ruby.rb.

$ git checkout master
Switched to branch 'master'
$ git mv hello.rb ruby.rb
$ vim ruby.rb 
$ git diff
diff --git a/ruby.rb b/ruby.rb
index 2aabb6e..bf64b17 100644
--- a/ruby.rb
+++ b/ruby.rb
@@ -1,7 +1,7 @@
 class HelloWorld

   def self.hello
-    puts "Hello World"
+    puts "Hello World from Ruby"
   end

 end
$ git commit -am 'added from ruby'
[master b7ae93b] added from ruby
 1 files changed, 1 insertions(+), 1 deletions(-)
 rename hello.rb => ruby.rb (65%)

Now those changes are recorded in the 'master' branch. Notice that the class name is back to 'HelloWorld', not 'HiWorld'. To incorporate the 'HiWorld' change we can just merge in the 'change_class' branch. However, the name of the file has changed since we branched, what will Git do?

$ git branch
  change_class
* master
$ git merge change_class
Renaming hello.rb => ruby.rb
Auto-merging ruby.rb
Merge made by recursive.
 ruby.rb |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)
$ cat ruby.rb
class HiWorld
  def self.hello
    puts "Hello World from Ruby"
  end
end

HiWorld.hello

Well, it will just figure it out. Notice that there are no merge conflicts and the file that had been renamed now has the 'HiWorld' class name change that was done in the other branch. Pretty cool.

merge conflicts

So, Git merges are magical, we never ever have to deal with merge conflicts again, right? Not quite. In situations where the same block of code is edited in different branches there is no way for a computer to figure it out, so it's up to us. Let's see another example of changing the same line in two branches.

$ git branch
* master
$ git checkout -b fix_readme
Switched to a new branch 'fix_readme'
$ vim README 
$ git commit -am 'fixed readme title'
[fix_readme 3ac015d] fixed readme title
 1 files changed, 1 insertions(+), 1 deletions(-)

Now we have committed a change to one line in our README file in a branch. Now let's change the same line in a different way back on our 'master' branch.

$ git checkout master
Switched to branch 'master'
$ vim README 
$ git commit -am 'fixed readme title differently'
[master 3cbb6aa] fixed readme title differently
 1 files changed, 1 insertions(+), 1 deletions(-)

Now is the fun part - we will merge the first branch into our master branch, causing a merge conflict.

$ git merge fix_readme
Auto-merging README
CONFLICT (content): Merge conflict in README
Automatic merge failed; fix conflicts and then commit the result.
$ cat README 
<<<<<<< HEAD
Many Hello World Examples
=======
Hello World Lang Examples
>>>>>>> fix_readme

This project has examples of hello world in
nearly every programming language.

You can see that Git inserts standard merge conflict markers, much like Subversion, into files when it gets a merge conflict. Now it's up to us to resolve them. We will do it manually here, but check out git mergetool if you want Git to fire up a graphical mergetool (like kdiff3, emerge, p4merge, etc) instead.

$ vim README   # here I'm fixing the conflict
$ git diff
diff --cc README
index 9103e27,69cad1a..0000000
--- a/README
+++ b/README
@@@ -1,4 -1,4 +1,4 @@@
- Many Hello World Examples
 -Hello World Lang Examples
++Many Hello World Lang Examples

  This project has examples of hello world in

A cool tip in doing merge conflict resolution in Git is that if you run git diff, it will show you both sides of the conflict and how you've resolved it as shown here. Now it's time to mark the file as resolved. In Git we do that with git add - to tell Git the file has been resolved you have to stage it.

$ git status -s
UU README
$ git add README 
$ git status -s
M  README
$ git commit 
[master 8d585ea] Merge branch 'fix_readme'

And now we've successfully resolved our merge conflict and committed the result.

In a nutshell you use git merge to combine another branch context into your current branch. It automatically figures out how to best combine the different snapshots into a new snapshot with the unique work of both.

So far we have been committing snapshots of your project and switching between different isolated contexts, but what if we've forgotten how we've got to where we are? Or what if we want to know how one branch differs from another? Git provides a tool that shows you all the commit messages that have lead up to the snapshot you are currently on, which is called git log.

To understand the log command, you have to understand what information is stored when you run the git commit command to store a snapshot. In addition to the manifest of files and commit message and information about the person who committed it, Git also stores the commit that you based this snapshot on. That is, if you clone a project, what was the snapshot that you modified to get to the snapshot that you saved? This is helpful to give context to how the project got to where it is and allows Git to figure out who changed what. If Git has the snapshot you save and the one you based it on, then it can automatically figure out what you changed. The commit that a new commit was based on is called the "parent".

To see a chronological list of the parents of any branch, you can run git log when you are in that branch. For example, if we run git log in the Hello World project that we have been working on in this section, we'll see all the commit messages that we've done.

$ git log
commit 8d585ea6faf99facd39b55d6f6a3b3f481ad0d3d
Merge: 3cbb6aa 3ac015d
Author: Scott Chacon <schacon@gmail.com>
Date:   Fri Jun 4 12:59:47 2010 +0200

    Merge branch 'fix_readme'

    Conflicts:
        README

commit 3cbb6aae5c0cbd711c098e113ae436801371c95e
Author: Scott Chacon <schacon@gmail.com>
Date:   Fri Jun 4 12:58:53 2010 +0200

    fixed readme title differently

commit 3ac015da8ade34d4c7ebeffa2053fcac33fb495b
Author: Scott Chacon <schacon@gmail.com>
Date:   Fri Jun 4 12:58:36 2010 +0200

    fixed readme title

commit 558151a95567ba4181bab5746bc8f34bd87143d6
Merge: b7ae93b 3467b0a
Author: Scott Chacon <schacon@gmail.com>
Date:   Fri Jun 4 12:37:05 2010 +0200

    Merge branch 'change_class'
...

To see a more compact version of the same history, we can use the --oneline option.

$ git log --oneline
8d585ea Merge branch 'fix_readme'
3cbb6aa fixed readme title differently
3ac015d fixed readme title
558151a Merge branch 'change_class'
b7ae93b added from ruby
3467b0a changed the class name
17f4acf first commit

What this is telling us is that this is the history of the development of this project. If the commit messages are descriptive, this can inform us as to what all changes have been applied or have influenced the current state of the snapshot and thus what is in it.

We can also use it to see when the history was branched and merged with the very helpful --graph option. Here is the same command but with the topology graph turned on:

$ git log --oneline --graph
*   8d585ea Merge branch 'fix_readme'
|\
| * 3ac015d fixed readme title
* | 3cbb6aa fixed readme title differently
|/
*   558151a Merge branch 'change_class'
|\
| * 3467b0a changed the class name
* | b7ae93b added from ruby
|/
* 17f4acf first commit

Now we can more clearly see when effort diverged and then was merged back together. This is very nice for seeing what has happened or what changes are applied, but it is also incredibly useful for managing your branches. Let's create a new branch, do some work in it and then switch back and do some work in our master branch, then see how the log command can help us figure out what is happening on each.

First we'll create a new branch to add the Erlang programming language Hello World example - we want to do this in a branch so that we don't muddy up our stable branch with code that may not work for a while so we can cleanly switch in and out of it.

$ git checkout -b erlang
Switched to a new branch 'erlang'
$ vim erlang_hw.erl
$ git add erlang_hw.erl 
$ git commit -m 'added erlang'
[erlang ab5ab4c] added erlang
 1 files changed, 5 insertions(+), 0 deletions(-)
 create mode 100644 erlang_hw.erl

Since we're having fun playing in functional programming languages we get caught up in it and also add a Haskell example program while still in the branch named 'erlang'.

$ vim haskell.hs
$ git add haskell.hs 
$ git commit -m 'added haskell'
[erlang 1834130] added haskell
 1 files changed, 4 insertions(+), 0 deletions(-)
 create mode 100644 haskell.hs

Finally, we decide that we want to change the class name of our Ruby program back to the way it was. So, we can go back to the master branch and change that and we decide to just commit it directly in the master branch instead of creating another branch.

$ git checkout master
Switched to branch 'master'
$ ls
README  ruby.rb
$ vim ruby.rb 
$ git commit -am 'reverted to old class name'
[master 594f90b] reverted to old class name
 1 files changed, 2 insertions(+), 2 deletions(-)

So, now say we don't work on the project for a while, we have other things to do. When we come back we want to know what the 'erlang' branch is all about and where we've left off on the master branch. Just by looking at the branch name, we can't know that we made Haskell changes in there, but using git log we easily can. If you give Git a branch name, it will show you just the commits that are "reachable" in the history of that branch, that is the commits that influenced the final snapshot.

$ git log --oneline erlang
1834130 added haskell
ab5ab4c added erlang
8d585ea Merge branch 'fix_readme'
3cbb6aa fixed readme title differently
3ac015d fixed readme title
558151a Merge branch 'change_class'
b7ae93b added from ruby
3467b0a changed the class name
17f4acf first commit

This way, it's pretty easy to see that we have Haskell code included in the branch (highlighted in the output). What is even cooler is that we can easily tell Git that we only are interested in the commits that are reachable in one branch that are not reachable in another, in other words which commits are unique to a branch in comparison to another.

In this case if we are interested in merging in the 'erlang' branch we want to see what commits are going to effect our snapshot when we do that merge. The way we tell Git that is by putting a ^ in front of the branch that we don't want to see. For instance, if we want to see the commits that are in the 'erlang' branch that are not in the 'master' branch, we can do erlang ^master, or vice versa. Note that the Windows command-line treats ^ as a special character, in which case you'll need to surround ^master in quotes.

$ git log --oneline erlang ^master
1834130 added haskell
ab5ab4c added erlang
$ git log --oneline master ^erlang
594f90b reverted to old class name

This gives us a nice, simple branch management tool. It allows us to easily see what commits are unique to which branches so we know what we're missing and what we would be merging in if we were to do a merge.

In a nutshell you use git log to list out the commit history or list of changes people have made that have lead to the snapshot at the tip of the branch. This allows you to see how the project in that context got to the state that it is currently in.

If you get to a point that is important and you want to forever remember that specific commit snapshot, you can tag it with git tag. The tag command will basically put a permanent bookmark at a specific commit so you can use it to compare to other commits in the future. This is often done when you cut a release or ship something.

Let's say we want to release our Hello World project as version "1.0". We can tag the last commit (HEAD) as "v1.0" by running git tag -a v1.0. The -a means "make an annotated tag", which allows you to add a tag message to it, which is what you almost always want to do. Running this without the -a works too, but it doesn't record when it was tagged, who tagged it, or let you add a tag message. It's recommended you always create annotated tags.

$ git tag -a v1.0 

When you run the git tag -a command, Git will open your editor and have you write a tag message, just like you would write a commit message.

Now, notice when we run git log --decorate, we can see our tag there.

$ git log --oneline --decorate --graph
* 594f90b (HEAD, tag: v1.0, master) reverted to old class name
*   8d585ea Merge branch 'fix_readme'
|\
| * 3ac015d (fix_readme) fixed readme title
* | 3cbb6aa fixed readme title differently
|/
*   558151a Merge branch 'change_class'
|\
| * 3467b0a changed the class name
* | b7ae93b added from ruby
|/
* 17f4acf first commit

If we do more commits, the tag will stay right at that commit, so we have that specific snapshot tagged forever and can always compare future snapshots to it.

We don't have to tag the commit that we're on, however. If we forgot to tag a commit that we released, we can retroactively tag it by running the same command, but with the commit SHA at the end. For example, say we had released commit 558151a (several commits back) but forgot to tag it at the time. We can just tag it now:

$ git tag -a v0.9 558151a
$ git log --oneline --decorate --graph
* 594f90b (HEAD, tag: v1.0, master) reverted to old class name
*   8d585ea Merge branch 'fix_readme'
|\
| * 3ac015d (fix_readme) fixed readme title
* | 3cbb6aa fixed readme title differently
|/
*   558151a (tag: v0.9) Merge branch 'change_class'
|\
| * 3467b0a changed the class name
* | b7ae93b added from ruby
|/
* 17f4acf first commit

Tags pointing to objects tracked from branch heads will be automatically downloaded when you fetch from a remote repository. However, tags that aren't reachable from branch heads will be skipped. If you want to make sure all tags are always included, you must include the --tags option.

$ git fetch origin --tags
remote: Counting objects: 1832, done.
remote: Compressing objects: 100% (726/726), done.
remote: Total 1519 (delta 1000), reused 1202 (delta 764)
Receiving objects: 100% (1519/1519), 1.30 MiB | 1.21 MiB/s, done.
Resolving deltas: 100% (1000/1000), completed with 182 local objects.
From git://github.com:example-user/example-repo
 * [new tag]         v1.0       -> v1.0
 * [new tag]         v1.1       -> v1.1

If you just want a single tag, use git fetch <remote> tag <tag-name>.

By default, tags are not included when you push to a remote repository. In order to explicitly update these you must include the --tags option when using git push.

In a nutshell you use git tag to mark a commit or point in your repo as important. This also allows you to refer to that commit with a more memorable reference than a SHA.