Revision control software are also known as Version Control Software (VCS), and by a few other names.

Git is the most widely used RCS today. Other RCS tools include Mercurial, Subversion (SVN), Perforce, CVS (Concurrent Versions System), Bazaar, TFS (Team Foundation Server), and Clearcase.

Github is a web-based project hosting platform for projects using Git for revision control. Other similar services include GitLab, BitBucket, and SourceForge.

Let's take your first few steps in your Git journey.

1. First, install Sourcetree (installation instructions), which is Git + a GUI for Git. If you prefer to use Git via the command line (i.e., without a GUI), you can install Git instead.

2. Next, create a directory for the repo (e.g., a directory named things).

3. Then, initialize a repository in that directory.

Sourcetree

Windows: Click File → Clone/New…. Click on Create button.
Mac: New... → Create New Repository.

Enter the location of the directory (Windows version shown below) and click Create.

Go to the things folder and observe how a hidden folder .git has been created.

Windows: you might have to configure Windows Explorer to show hidden files.

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CLI

Open a Git Bash Terminal.

If you installed Sourcetree, you can click the Terminal button to open a GitBash terminal (on a Linux/Mac environment, even a regular terminal should do).

Navigate to the things directory.
Use the command git init which should initialize the repo.

$ cd /c/repos/things
$ git init

    

    


    
    

Initialized empty Git repository in c:/repos/things/.git/

    

    


    
    

You can use the list all command ls -a to view all files, which should show the .git directory that was created by the previous command.

$ ls -a
.  ..  .git

    

    


    
    

You can also use the git status command to check the status of the newly-created repo. It should respond with something like the following:

$ git status

    

    


    
    

# On branch master
#
# No commits yet
#
nothing to commit (create/copy files and use "git add" to track)

    

    


    
    

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Tracking and ignoring

In a repo, you can specify which files to track and which files to ignore. Some files such as temporary log files created during the build/test process should not be revision-controlled.

Staging and committing

After initializing a repository, Git can help you with revision controlling files inside the working directory. However, it is not automatic. You need to tell Git which of your changes (aka revisions) should be committed to its memory for later use. Saving changes into Git's memory in that way is called committing and a change saved to the revision history is called a commit.

Here are the steps you can follow to learn how to create Git commits:

1. Do some changes to the content inside the working directory e.g., create a file named fruits.txt in the things directory and add some dummy text to it.

2. Observe how the file is detected by Git.

Sourcetree

The file is shown as ‘unstaged’.

---

CLI

You can use the git status command to check the status of the working directory.

$ git status

    

    


    
    

# On branch master
#
# No commits yet
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#   a.txt
nothing added to commit but untracked files present (use "git add" to track)

    

    


    
    

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3. Stage the changes to commit: Although Git has detected the file in the working directory, it will not do anything with the file unless you tell it to. Suppose you want to commit the current changes to the file. First, you should stage the file, which is how you tell Git which changes you want to include in the next commit.

Sourcetree

Select the fruits.txt and click on the Stage Selected button.

fruits.txt should appear in the Staged files panel now.

If Sourcetree shows a \ No newline at the end of the file message below the staged lines (i.e., below the cherries line in the above screenshot), that is because you did not hit enter after entering the last line of the file (hence, Git is not sure if that line is complete). To rectify, move the cursor to end of the last line in that file and hit enter (like you are adding a blank line below it). This new change will now appear as an 'unstaged' change. Stage it as well.

---

CLI

You can use the stage or the add command (they are synonyms, add is the more popular choice) to stage files.

$ git add fruits.txt
$ git status

    

    


    
    

# On branch master
#
# No commits yet
#
# Changes to be committed:
#   (use "git rm --cached <file>..." to unstage)
#
#       new file:   fruits.txt
#

    

    


    
    

---

4. Commit the staged version of fruits.txt.

Sourcetree

Click the Commit button, enter a commit message e.g. add fruits.txt into the text box, and click Commit.

---

CLI

Use the commit command to commit. The -m switch is used to specify the commit message.

$ git commit -m "Add fruits.txt"

    

    


    
    

You can use the log command to see the commit history.

$ git log

    

    


    
    

commit 8fd30a6910efb28bb258cd01be93e481caeab846
Author: … < … @... >
Date:   Wed Jul 5 16:06:28 2017 +0800

  Add fruits.txt

    

    


    
    

---

Note the existence of something called the master branch. Git uses a mechanism called branches to facilitate evolving file content in parallel (we'll learn git branching in a later topic). Furthermore, Git auto-creates a branch named master on which the commits go on by default.

Sourcetree

Expand the BRANCHES menu and click on the master to view the history graph, which contains only one node at the moment, representing the commit you just added. Also note a label master attached to the commit.

This label points to the latest commit on the master branch.

---

CLI

Run the git status command and note how the output contains the phrase on branch master.

---

5. Do a few more commits.

1. Make some changes to fruits.txt (e.g. add some text and delete some text). Stage the changes, and commit the changes using the same steps you followed before. You should end up with something like this.

   

2. Next, add two more files colors.txt and shapes.txt to the same working directory. Add a third commit to record the current state of the working directory.

   
   You can decide what to stage and what to leave unstaged. When staging changes to commit, you can leave some files unstaged, if you wish to not include them in the next commit. In fact, Git even allows some changes in a file to be staged, while others changes in the same file to be unstaged. This flexibility is particularly useful when you want to put all related changes into a commit while leaving out unrelated changes.

6. See the revision graph: Note how commits form a path-like structure aka the revision tree/graph. In the revision graph, each commit is shown as linked to its 'parent' commit (i.e., the commit before it).

Sourcetree

To see the revision graph, click on the History item (listed under the WORKSPACE section) on the menu on the right edge of Sourcetree.

---

CLI

The gitk command opens a rudimentary graphical view of the revision graph.

---

How do undo/delete a commit?

Sourcetree

To undo the last commit, right-click on the commit just before it, and choose Reset current branch to this commit.

In the next dialog, choose the mode Mixed - keep working copy but reset index option. This will make the offending commit disappear but will keep the changes that you included in that commit intact.

If you use the Soft - ... mode instead, the last commit will be undone as before, but the changes included in that commit will stay in the staging area.

To delete the last commit entirely (i.e., undo the commit and also discard the changes included in that commit), do as above but choose the Hard - ... mode instead.

To undo/delete last n commits, right-click on the commit just before the last n commits, and do as above.

---

CLI

To undo the last commit, but keep the changes in the staging area, use the following command.

$ git reset --soft HEAD~1

    

    


    
    

To undo the last commit, and remove the changes from the staging area (but not discard the changes), used --mixed instead of --soft.

$ git reset --mixed HEAD~1

    

    


    
    

To delete the last commit entirely (i.e., undo the commit and also discard the changes included in that commit), do as above but use the --hard flag instead (i.e., do a hard reset).

$ git reset --hard HEAD~1

    

    


    
    

To undo/delete last n commits: HEAD~1 is used to tell get you are targeting the commit one position before the latest commit -- in this case the target commit is the one we want to reset to, not the one we want to undo (as the command used is reset). To undo/delete two last commits, you can use HEAD~2, and so on.

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Often, there are files inside the Git working folder that you don't want to revision-control e.g., temporary log files. Follow the steps below to learn how to configure Git to ignore such files.

1. Add a file into your repo's working folder that you supposedly don't want to revision-control e.g., a file named temp.txt. Observe how Git has detected the new file.

2. Configure Git to ignore that file:

temp.txt

    

    


    
    

temp.txt

    

    


    
    

Files recommended to be omitted from version control

• Binary files generated when building your project e.g., *.class, *.jar, *.exe (reasons: 1. no need to version control these files as they can be generated again from the source code 2. Revision control systems are optimized for tracking text-based files, not binary files.
• Temporary files e.g., log files generated while testing the product
• Local files i.e., files specific to your own computer e.g., local settings of your IDE
• Sensitive content i.e., files containing sensitive/personal information e.g., credential files, personal identification data (especially, if there is a possibility of those files getting leaked via the revision control system).

RCS tools store the history of the working directory as a series of commits. This means you should commit after each change that you want the RCS to 'remember'.

Each commit in a repo is a recorded point in the history of the project that is uniquely identified by an auto-generated hash e.g. a16043703f28e5b3dab95915f5c5e5bf4fdc5fc1.

You can tag a specific commit with a more easily identifiable name e.g. v1.0.2.

To see what changed between two points of the history, you can ask the RCS tool to diff the two commits in concern.

To restore the state of the working directory at a point in the past, you can checkout the commit in concern. i.e., you can traverse the history of the working directory simply by checking out the commits you are interested in.

Each Git commit is uniquely identified by a hash e.g., d670460b4b4aece5915caf5c68d12f560a9fe3e4. As you can imagine, using such an identifier is not very convenient for our day-to-day use. As a solution, Git allows adding a more human-readable tag to a commit e.g., v1.0-beta.

Here's how you can tag a commit in a local repo:

Sourcetree

Right-click on the commit (in the graphical revision graph) you want to tag and choose Tag….

Specify the tag name e.g. v1.0 and click Add Tag.

The added tag will appear in the revision graph view.

---

CLI

To add a tag to the current commit as v1.0:

$ git tag –a v1.0

    

    


    
    

To view tags:

$ git tag

    

    


    
    

To learn how to add a tag to a past commit, go to the ‘Git Basics – Tagging’ page of the git-scm book and refer the ‘Tagging Later’ section.

---

After adding a tag to a commit, you can use the tag to refer to that commit, as an alternative to using the hash.

Git can show you what changed in each commit.

Sourcetree

To see which files changed in a commit, click on the commit. To see what changed in a specific file in that commit, click on the file name.

---

CLI

$ git show < part-of-commit-hash >

    

    


    
    

Example:

$ git show 5bc0e306

    

    


    
    

commit 5bc0e30635a754908dbdd3d2d833756cc4b52ef3
Author: … < … >
Date:   Sat Jul 8 16:50:27 2017 +0800

    fruits.txt: replace banana with berries

diff --git a/fruits.txt b/fruits.txt
index 15b57f7..17f4528 100644
--- a/fruits.txt
+++ b/fruits.txt
@@ -1,3 +1,3 @@
 apples
-bananas
+berries
 cherries

    

    


    
    

---

Git can also show you the difference between two points in the history of the repo.

Sourcetree

Select the two points you want to compare using Ctrl+Click. The differences between the two selected versions will show up in the bottom half of Sourcetree, as shown in the screenshot below.

The same method can be used to compare the current state of the working directory (which might have uncommitted changes) to a point in the history.

---

CLI

The diff command can be used to view the differences between two points of the history.

• git diff: shows the changes (uncommitted) since the last commit.
• git diff 0023cdd..fcd6199: shows the changes between the points indicated by commit hashes.
  Note that when using a commit hash in a Git command, you can use only the first few characters (e.g., first 7-10 chars) as that's usually enough for Git to locate the commit.
• git diff v1.0..HEAD: shows changes that happened from the commit tagged as v1.0 to the most recent commit.

Resources

• Git-Tower Tutorial: Inspecting Changes with Diffs
• How to view the next page of a git command result

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---

Git can load a specific version of the history to the working directory. Note that if you have uncommitted changes in the working directory, you need to stash them first to prevent them from being overwritten.

Sourcetree

Double-click the commit you want to load to the working directory, or right-click on that commit and choose Checkout....

Click OK to the warning about ‘detached HEAD’ (similar to below).

The specified version is now loaded to the working folder, as indicated by the HEAD label. HEAD is a reference to the currently checked out commit.

If you checkout a commit that comes before the commit in which you added the .gitignore file, Git will now show ignored files as ‘unstaged modifications’ because at that stage Git hasn’t been told to ignore those files.

To go back to the latest commit, double-click it.

---

CLI

Use the checkout <commit-identifier> command to change the working directory to the state it was in at a specific past commit.

• git checkout v1.0: loads the state as at commit tagged v1.0
• git checkout 0023cdd: loads the state as at commit with the hash 0023cdd
• git checkout HEAD~2: loads the state that is 2 commits behind the most recent commit

For now, you can ignore the warning about ‘detached HEAD’.

---

You can use Git's stash feature to temporarily shelve (or stash) changes you've made to your working copy so that you can work on something else, and then come back and re-apply the stashed changes later on. _{-- adapted from Atlassian}

Remote repositories are repos that are hosted on remote computers and allow remote access. They are especially useful for sharing the revision history of a codebase among team members of a multi-person project. They can also serve as a remote backup of your codebase.

It is possible to set up your own remote repo on a server, but the easier option is to use a remote repo hosting service such as GitHub or BitBucket.

When you clone from a repo, the original repo is commonly referred to as the upstream repo. A repo can have multiple upstream repos. For example, let's say a repo repo1 was cloned as repo2 which was then cloned as repo3. In this case, repo1 and repo2 are upstream repos of repo3.

Cloning, pushing, and pulling can be done between two local repos too, although it is more common for them to involve a remote repo.

Given below is an example scenario you can try yourself to learn Git cloning.

Suppose you want to clone the sample repo samplerepo-things to your computer.

Here's a scenario you can try in order to learn how to pull commits from another repo to yours.

1. Clone a repo (e.g., the repo used in [Git & GitHub → Clone]) to be used for this activity.

2. Delete the last few commits to simulate cloning the repo a few commits ago.

Sourcetree

Right-click the target commit (i.e. the commit that is 2 commits behind the tip) and choose Reset current branch to this commit.

Choose the Hard - … option and click OK.

This is what you will see.

Note the following (cross-refer the screenshot above):

Arrow marked as a: The local repo is now at this commit, marked by the master label.
Arrow marked as b: The origin/master label shows what is the latest commit in the master branch in the remote repo. origin is the default name given to the upstream repo you cloned from.

---

CLI

Use the reset command to delete commits at the tip of the revision history.

$ git reset --hard HEAD~2

    

    


    
    

More info on the git reset command can be found here.

---

Now, your local repo state is exactly how it would be if you had cloned the repo 2 commits ago, as if somebody has added two more commits to the remote repo since you cloned it.

3. Pull from the other repo: To get those missing commits to your local repo (i.e. to sync your local repo with upstream repo) you can do a pull.

Sourcetree

Click the Pull button in the main menu, choose origin and master in the next dialog, and click OK.

Now you should see something like this where master and origin/master are both pointing the same commit.

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CLI

$ git pull origin

    

    


    
    

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You can also do a fetch instead of a pull in which case the new commits will be downloaded to your repo but the working directory will remain at the current commit. To move the current state to the latest commit that was downloaded, you need to do a merge. A pull is a shortcut that does both those steps in one go.

Given below is a scenario you can try in order to learn how to fork a repo:.

0. Create a GitHub account if you don't have one yet.

1. Go to the GitHub repo you want to fork e.g., samplerepo-things

2. Click on the button on the top-right corner. In the next step,

• choose to fork to your own account or to another GitHub organization that you are an admin of.
• Un-tick the [ ] Copy the master branch only option, so that you get copies of other branches (if any) in the repo.

Branching is the process of evolving multiple versions of the software in parallel. For example, one team member can create a new branch and add an experimental feature to it while the rest of the team keeps working on another branch. Branches can be given names e.g. master, release, dev.

A branch can be merged into another branch. Merging usually results in a new commit that represents the changes done in the branch being merged.

Branching and merging

Merge conflicts happen when you try to merge two branches that had changed the same part of the code and the RCS cannot decide which changes to keep. In those cases, you have to ‘resolve’ the conflicts manually.

Git supports branching, which allows you to do multiple parallel changes to the content of a repository.

First, let us learn how the repo looks like as you perform branching operations.

A Git branch is simply a named label pointing to a commit. The HEAD label indicates which branch you are on. Git creates a branch named master by default. When you add a commit, it goes into the branch you are currently on, and the branch label (together with the HEAD label) moves to the new commit.

Given below is an illustration of how branch labels move as branches evolve. Refer to the text below it for explanations of each stage.

1. There is only one branch (i.e., master) and there is only one commit on it. The HEAD label is pointing to the master branch (as we are currently on that branch).

   To learn a bit more about how labels such as master and HEAD work, you can refer to this article.

2. A new commit has been added. The master and the HEAD labels have moved to the new commit.

3. A new branch fix1 has been added. The repo has switched to the new branch too (hence, the HEAD label is attached to the fix1 branch).

4. A new commit (c) has been added. The current branch label fix1 moves to the new commit, together with the HEAD label.

5. The repo has switched back to the master branch. Hence, the HEAD has moved back to master branch's .
   At this point, the repo's working directory reflects the code at commit b (not c).

6. A new commit (d) has been added. The master and the HEAD labels have moved to that commit.
7. The repo has switched back to the fix1 branch and added a new commit (e) to it.
8. The repo has switched to the master branch and the fix1 branch has been merged into the master branch, creating a merge commit f. The repo is currently on the master branch.

Now that you have some idea how the repo will look like when branches are being used, let's follow the steps below to learn how to perform branching operations using Git. You can use any repo you have on your computer (e.g. a clone of the samplerepo-things) for this.

0. Observe that you are normally in the branch called master.

Sourcetree

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CLI

$ git status

    

    


    
    

on branch master

    

    


    
    

---

1. Start a branch named feature1 and switch to the new branch.

Sourcetree

Click on the Branch button on the main menu. In the next dialog, enter the branch name and click Create Branch.

Note how the feature1 is indicated as the current branch (reason: Sourcetree automatically switches to the new branch when you create a new branch).

---

CLI

You can use the branch command to create a new branch and the checkout command to switch to a specific branch.

$ git branch feature1
$ git checkout feature1

    

    


    
    

One-step shortcut to create a branch and switch to it at the same time:

$ git checkout –b feature1

    

    


    
    

---

2. Create some commits in the new branch. Just commit as per normal. Commits you add while on a certain branch will become part of that branch.
Note how the master label and the HEAD label moves to the new commit (The HEAD label of the local repo is represented as in Sourcetree).

3. Switch to the master branch. Note how the changes you did in the feature1 branch are no longer in the working directory.

Sourcetree

Double-click the master branch.

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CLI

$ git checkout master

    

    


    
    

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4. Add a commit to the master branch. Let’s imagine it’s a bug fix.
To keep things simple for the time being, this commit should not involve the same content that you changed in the feature1 branch. To be on the safe side, you can change an entirely different file in this commit.

5. Switch back to the feature1 branch (similar to step 3).

6. Merge the master branch to the feature1 branch, giving an end-result like the following. Also note how Git has created a merge commit.

$ git merge master

    

    


    
    

The objective of that merge was to sync the feature1 branch with the master branch. Observe how the changes you did in the master branch (i.e. the imaginary bug fix) is now available even when you are in the feature1 branch.

To undo a merge,

1. Ensure you are in the branch that received the merge.
2. Do a hard reset (similar to how you delete a commit) of that branch to the commit that would be the tip of that branch had you not done the offending merge.

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In the example below, you merged master to feature1.

If you want to undo that merge,

1. Ensure you are in the feature1 branch.
2. Reset the feature1 branch to the commit highlighted in the screenshot above (because that was the tip of the feature1 branch before you merged the master branch to it.

7. Add another commit to the feature1 branch.

8. Switch to the master branch and add one more commit.

9. Merge feature1 to the master branch, giving and end-result like this:

$ git merge feature1

    

    


    
    

10. Create a new branch called add-countries, switch to it, and add some commits to it (similar to steps 1-2 above). You should have something like this now:

11. Go back to the master branch and merge the add-countries branch onto the master branch (similar to steps 8-9 above). While you might expect to see something like the following,

... you are likely to see something like this instead:

That is because Git does a fast forward merge if possible. Seeing that the master branch has not changed since you started the add-countries branch, Git has decided it is simpler to just put the commits of the add-countries branch in front of the master branch, without going into the trouble of creating an extra merge commit.

It is possible to force Git to create a merge commit even if fast forwarding is possible.

Sourcetree

Tick the box shown below when you merge a branch:

---

CLI

Use the --no-ff switch (short for no fast forward):

$ git merge --no-ff add-countries

    

    


    
    

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Merge conflicts happen when you try to combine two incompatible versions (e.g., merging a branch to another but each branch changed the same part of the code in a different way).

Here are the steps to simulate a merge conflict and use it to learn how to resolve merge conflicts.

0. Create an empty repo or clone an existing repo, to be used for this activity.

1. Start a branch named fix1 in the repo. Create a commit that adds a line with some text to one of the files.

2. Switch back to master branch. Create a commit with a conflicting change i.e. it adds a line with some different text in the exact location the previous line was added.

3. Try to merge the fix1 branch onto the master branch. Git will pause mid-way during the merge and report a merge conflict. If you open the conflicted file, you will see something like this:

COLORS
------
blue
<<<<<< HEAD
black
=======
green
>>>>>> fix1
red
white

    

    


    
    

4. Observe how the conflicted part is marked between a line starting with <<<<<< and a line starting with >>>>>>, separated by another line starting with =======.

Highlighted below is the conflicting part that is coming from the master branch:

blue
<<<<<< HEAD
black
=======
green
>>>>>> fix1
red

    

    


    
    

This is the conflicting part that is coming from the fix1 branch:

blue
<<<<<< HEAD
black
=======
green
>>>>>> fix1
red

    

    


    
    

5. Resolve the conflict by editing the file. Let us assume you want to keep both lines in the merged version. You can modify the file to be like this:

COLORS
------
blue
black
green
red
white

    

    


    
    

6. Stage the changes, and commit. You have now successfully resolved the merge conflict.

Git branches in a local repo can be linked to a branch in a remote repo so the local branch can 'track' the corresponding remote branch, and revision history contained in the local and the remote branch pair can be synchronized as desired.

[A] Pushing a new branch to a remote repo

Let's see how you can push a branch that you created in your local repo to the remote repo. Note that this branch does not exist in the remote repo yet.

Given below is how to push a branch named add-intro to your own fork named samplerepo-pr-practice.

We assume that your local repo already has the remote added to it with the name origin. If that is not the case, you should first configure your local repo to be able to communicate with the target remote repo.

Sourcetree

1. Click on Push button, which opens up the Push dialog.
2. Choose the remote that you wish to push the branch (assuming you've added that repo to your Sourcetree already).
3. Select the branch(es) you want to push -- in this case, add-intro.
   Ensure the Track? checkbox is ticked for the selected branch(es).
4. Click Push.

---

CLI

$ git push -u origin add-intro

    

    


    
    

The -u (or --update) flag tells Git that you wish the local branch to 'track' the remote branch that will be created as a result of this push.

See git-scm.com/docs/git-push for details of the push command.

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[B] Pulling a remote branch for the first time

Here, let's see how to fetch a new branch (i.e., it does not exist in your local repo yet) from a remote repo.

Sourcetree

1. Check the list of remote branches by expanding the REMOTES menu on the left edge of Sourcetree. If the branch you expected to find is missing, you can click the Fetch button (in the top toolbar) to refresh the information shown under remotes.

2. Double-click the branch name (e.g., tweak-requirements branch in the myfork remote), which should open the checkout dialog shown below.

3. Go with the default settings (shown above) should be fine. Once you click OK, the branch will appear in your local repo. Furthermore, that repo will switch to that branch, and the local branch will the remote branch as well.

---

CLI

1. Fetch details from the remote. e.g., if the remote is named myfork

$ git fetch myfork

    

    


    
    

2. List the branches to see the name of the branch you want to pull.

$ git branch -a

    

    


    
    

master
remotes/myfork/master
remotes/myfork/branch1

    

    


    
    

-a flag tells Git to list both local and remote branches.

3. Create a matching local branch and switch to it.

$ git switch -c branch1 myfork/branch1

    

    


    
    

Switched to a new branch 'branch1'
branch 'branch1' set up to track 'myfork/branch1'.

    

    


    
    

-c flag tells Git to create a new local branch.

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[C] Syncing branches

In this section we assume that you have a local branch that is already tracking a remote branch (e.g., as a result of doing [A] or [B] above).

To push new changes in the local branch to the corresponding remote branch:

Sourcetree

Similar to how you pushed a new branch (in [A]):

---

CLI

Similar to [A] above, but omit the -u flag. e.g.,

$ git push origin add-intro

    

    


    
    

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If you push but the remote branch has new commits that you don't have locally, Git will abort the push and will ask you to pull first.

To pull new changes from a remote branch to the corresponding local branch:

Sourcetree

1. Switch to the branch you want to update by double-clicking the branch name. e.g.,

2. Pull the updated in the remote branch to the local branch by right-clicking on the branch name (in the same place as above), and choosing Pull <remote>/<branch> (tracked) e.g., Pull myfork/add-intro (tracked).

---

CLI

1. Switch to the branch you want to update using git checkout <branch> e.g.,

$ git checkout branch1

    

    


    
    

2. Pull the updated in the remote branch to the local branch, using git pull <remote> <branch> e.g.,

$ git pull origin branch1

    

    


    
    

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If you pull but your local branch has new commits the remote branch doesn't have, Git will automatically perform a merge between the local branch and the remote branch.