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Windows の場合, 標準で SSH を使用することができない関係で, SourceTreeに SSH に関するものがまとめて付属しているのですが, Mac ではついていません. (SSH 接続の際OS側のOpenSShを使用するため) ので, ターミナルを操作して SSH キー生成を行なっていきます. I am unable to clone via SourceTree at all. I am able to run 'git clone' from the commandline to clone this repository. Once I do, I am able to add it as a Working Directory in SourceTree.

Version control, also known as source control, is the practice of tracking and managing changes to software code. Version control systems are software tools that help software teams manage changes to source code over time. As development environments have accelerated, version control systems help software teams work faster and smarter. They are especially useful for DevOps teams since they help them to reduce development time and increase successful deployments.

Version control software keeps track of every modification to the code in a special kind of database. If a mistake is made, developers can turn back the clock and compare earlier versions of the code to help fix the mistake while minimizing disruption to all team members.

For almost all software projects, the source code is like the crown jewels - a precious asset whose value must be protected. For most software teams, the source code is a repository of the invaluable knowledge and understanding about the problem domain that the developers have collected and refined through careful effort. Version control protects source code from both catastrophe and the casual degradation of human error and unintended consequences.

Software developers working in teams are continually writing new source code and changing existing source code. The code for a project, app or software component is typically organized in a folder structure or 'file tree'. One developer on the team may be working on a new feature while another developer fixes an unrelated bug by changing code, each developer may make their changes in several parts of the file tree.

Version control helps teams solve these kinds of problems, tracking every individual change by each contributor and helping prevent concurrent work from conflicting. Changes made in one part of the software can be incompatible with those made by another developer working at the same time. This problem should be discovered and solved in an orderly manner without blocking the work of the rest of the team. Further, in all software development, any change can introduce new bugs on its own and new software can't be trusted until it's tested. So testing and development proceed together until a new version is ready.

Good version control software supports a developer's preferred workflow without imposing one particular way of working. Ideally it also works on any platform, rather than dictate what operating system or tool chain developers must use. Great version control systems facilitate a smooth and continuous flow of changes to the code rather than the frustrating and clumsy mechanism of file locking - giving the green light to one developer at the expense of blocking the progress of others.

Software teams that do not use any form of version control often run into problems like not knowing which changes that have been made are available to users or the creation of incompatible changes between two unrelated pieces of work that must then be painstakingly untangled and reworked. If you're a developer who has never used version control you may have added versions to your files, perhaps with suffixes like 'final' or 'latest' and then had to later deal with a new final version. Perhaps you've commented out code blocks because you want to disable certain functionality without deleting the code, fearing that there may be a use for it later. Version control is a way out of these problems.

Version control software is an essential part of the every-day of the modern software team's professional practices. Individual software developers who are accustomed to working with a capable version control system in their teams typically recognize the incredible value version control also gives them even on small solo projects. Once accustomed to the powerful benefits of version control systems, many developers wouldn't consider working without it even for non-software projects.

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Benefits of version control systems

Using version control software is a best practice for high performing software and DevOps teams. Version control also helps developers move faster and allows software teams to preserve efficiency and agility as the team scales to include more developers.

Version Control Systems (VCS) have seen great improvements over the past few decades and some are better than others. VCS are sometimes known as SCM (Source Code Management) tools or RCS (Revision Control System). One of the most popular VCS tools in use today is called Git. Git is a Distributed VCS, a category known as DVCS, more on that later. Like many of the most popular VCS systems available today, Git is free and open source. Regardless of what they are called, or which system is used, the primary benefits you should expect from version control are as follows.

1. A complete long-term change history of every file. This means every change made by many individuals over the years. Changes include the creation and deletion of files as well as edits to their contents. Different VCS tools differ on how well they handle renaming and moving of files. This history should also include the author, date and written notes on the purpose of each change. Having the complete history enables going back to previous versions to help in root cause analysis for bugs and it is crucial when needing to fix problems in older versions of software. If the software is being actively worked on, almost everything can be considered an 'older version' of the software.

2. Branching and merging. Having team members work concurrently is a no-brainer, but even individuals working on their own can benefit from the ability to work on independent streams of changes. Creating a 'branch' in VCS tools keeps multiple streams of work independent from each other while also providing the facility to merge that work back together, enabling developers to verify that the changes on each branch do not conflict. Many software teams adopt a practice of branching for each feature or perhaps branching for each release, or both. There are many different workflows that teams can choose from when they decide how to make use of branching and merging facilities in VCS.

3. Traceability. Being able to trace each change made to the software and connect it to project management and bug tracking software such as Jira, and being able to annotate each change with a message describing the purpose and intent of the change can help not only with root cause analysis and other forensics. Having the annotated history of the code at your fingertips when you are reading the code, trying to understand what it is doing and why it is so designed can enable developers to make correct and harmonious changes that are in accord with the intended long-term design of the system. This can be especially important for working effectively with legacy code and is crucial in enabling developers to estimate future work with any accuracy.

While it is possible to develop software without using any version control, doing so subjects the project to a huge risk that no professional team would be advised to accept. So the question is not whether to use version control but which version control system to use.

There are many choices, but here we are going to focus on just one, Git. Learn more about other types of version control software.

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This page is an examination of the git checkout command. It will cover usage examples and edge cases. In Git terms, a 'checkout' is the act of switching between different versions of a target entity. The git checkout command operates upon three distinct entities: files, commits, and branches. In addition to the definition of 'checkout' the phrase 'checking out' is commonly used to imply the act of executing the git checkout command. In the Undoing Changes topic, we saw how git checkout can be used to view old commits. The focus for the majority of this document will be checkout operations on branches.

Checking out branches is similar to checking out old commits and files in that the working directory is updated to match the selected branch/revision; however, new changes are saved in the project history—that is, it’s not a read-only operation.

Checking out branches

The git checkout command lets you navigate between the branches created by git branch. Checking out a branch updates the files in the working directory to match the version stored in that branch, and it tells Git to record all new commits on that branch. Think of it as a way to select which line of development you’re working on.

Having a dedicated branch for each new feature is a dramatic shift from a traditional SVN workflow. It makes it ridiculously easy to try new experiments without the fear of destroying existing functionality, and it makes it possible to work on many unrelated features at the same time. In addition, branches also facilitate several collaborative workflows.

The git checkout command may occasionally be confused with git clone. The difference between the two commands is that clone works to fetch code from a remote repository, alternatively checkout works to switch between versions of code already on the local system.

Usage: Existing branches

Assuming the repo you're working in contains pre-existing branches, you can switch between these branches using git checkout. To find out what branches are available and what the current branch name is, execute git branch.

The above example demonstrates how to view a list of available branches by executing the git branch command, and switch to a specified branch, in this case, the feature_inprogress_branch.

New Branches

Git checkout works hand-in-hand with git branch. The git branch command can be used to create a new branch. When you want to start a new feature, you create a new branch off master using git branch new_branch. Once created you can then use git checkout new_branch to switch to that branch. Additionally, The git checkout command accepts a -b argument that acts as a convenience method which will create the new branch and immediately switch to it. You can work on multiple features in a single repository by switching between them with git checkout.

The above example simultaneously creates and checks out . The -b option is a convenience flag that tells Git to run git branch before running git checkout .

By default git checkout -b will base the new-branch off the current HEAD. An optional additional branch parameter can be passed to git checkout. In the above example, is passed which then bases new-branch off of existing-branch instead of the current HEAD.

Switching Branches

Switching branches is a straightforward operation. Executing the following will point HEAD to the tip of .

Git tracks a history of checkout operations in the reflog. You can execute git reflog to view the history.

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Git Checkout a Remote Branch

When collaborating with a team it is common to utilize remote repositories. These repositories may be hosted and shared or they may be another colleague's local copy. Each remote repository will contain its own set of branches. In order to checkout a remote branch you have to first fetch the contents of the branch.

In modern versions of Git, you can then checkout the remote branch like a local branch.

Older versions of Git require the creation of a new branch based on the remote.

Additionally you can checkout a new local branch and reset it to the remote branches last commit.

Detached HEADS

Now that we’ve seen the three main uses of git checkout on branches, it's important to discuss the “detached HEAD” state. Remember that the HEAD is Git’s way of referring to the current snapshot. Internally, the git checkout command simply updates the HEAD to point to either the specified branch or commit. When it points to a branch, Git doesn't complain, but when you check out a commit, it switches into a “detached HEAD” state.

This is a warning telling you that everything you’re doing is “detached” from the rest of your project’s development. If you were to start developing a feature while in a detached HEAD state, there would be no branch allowing you to get back to it. When you inevitably check out another branch (e.g., to merge your feature in), there would be no way to reference your feature:

The point is, your development should always take place on a branch—never on a detached HEAD. This makes sure you always have a reference to your new commits. However, if you’re just looking at an old commit, it doesn’t really matter if you’re in a detached HEAD state or not.

Summary

This page focused on usage of the git checkout command when changing branches. In summation, git checkout, when used on branches, alters the target of the HEAD ref. It can be used to create branches, switch branches, and checkout remote branches. The git checkout command is an essential tool for standard Git operation. It is a counterpart to git merge. The git checkout and git merge commands are critical tools to enabling git workflows.

Ready to try branching?

Try this interactive tutorial.