6.170 Tutorial 1 Git Prerequisites 1. Have Git installed and configured. (See: https://help.GitHub.com/articles/set-up-git) 2. Signup for a GitHub account. (http://www.github.com) Goals of this Tutorial 1. 2. 3. 4. Get familiar with source code version control using Git Create your first Git repository Learn useful Git commands to be used throughout the course Create a GitHub repository and learn to push/pull code from this repository Today’s Tutorial 1. What is Git? 1. A version control system for project code allows “snapshot” like functionality so that you can view and compare previous versions of your files. 2. Allows easy collaboration for source code development between team members. 3. “The purpose of Git is to manage a project, or a set of files, as they change over time. Git stores this information in a data structure called a repository.” [1] 2. How Git works 2.1 Core concept: Repository A Repository consists of : 1. A set of commit objects identified by a SHA1 name. Think of a commit as a snapshot in time of your project code. You can create as many commits as you want. 2. A set of references to commit objects. These references are called “heads”. (Not to be confused with HEAD (capitalized) which is a reference to the current head) A commit object consists of: 1. A set of files, reflecting the state of a project at a given point in time. 2. References to parent commit objects. 3. An SHA1 name, a 40character string that uniquely identifies the commit object. The name is composed of a hash of relevant aspects of the commit, so identical commits will always have the same name. 4. Example of a commit (obtained using “git log”): $ commit 034072dc2c02da0ab2872c0315a3f237027eb5e7 $ Author: Your Name\RXUQDPH#PLWHGX! $ Date: Sat Nov 10 17:08:57 2012 -0500 $ 1. Better Logging. 2. Schema changes 1 2.2 Simple Operations on Repositories 1. To create a repository, use “git init” a. $ mkdir b. $ cd c. $ git init d. This will create a “.git” directory in e. Note: This is your local repository and not necessarily shared with others. See image below for operations on local and remote repositories. Remote repositories are explained later in this tutorial. 2. To add files to the repository, use “git add ” followed by “git commit” a. $ cd b. $ echo ‘Hello World’ > hello1.txt c. $ echo ‘Hello MIT’ > hello2.txt d. $ echo ‘Hello 6.170’ > hello3.txt e. $ git add hello1.txt hello2.txt f. This tells Git to include both files “hello1.txt” and “hello2.txt” in the next commit to the repository. g. “git add .” works recursively and includes all files and subdirectories. Note: Use this recursive command cautiously. h. To include individual files, use “git add /path/to/file/” i. Wildcard could be used. “git add ‘*.txt’” will add all files with suffix txt. Note: need to use single quotes. j. $ git commit -a -m “Adding test files to the repository ” k. This will create a commit object consisting the two files and add them to the 2 repository along with the message specified by the “-m” flag. l. Note: “git add ” must be repeated before each “git commit” operation. 3. To check history of commits in your repository, use “git log” 4. To delete files from the repository, use “git rm” a. $ git rm hello1.txt b. This will remove hello1.txt from your repository as well as your local copy of hello1.txt 5. Lets do a few more operations locally: a. $ cd b. $ echo ‘Hello World! git rocks!’ >> hello2.txt c. $ rm hello3.txt 6. To check the current status of your project, use “git status” a. $ cd b. $ git status c. This will show all modified files, new files, and deleted files. 7. Comparing two versions of a file a. $ git diff hello2.txt b. This will show you the differences between your local version and the repository version of the file. c. To see differences between two previous commits, use “git diff []” 8. Unstaging a file (Removing a file from a commit) Before you push, if you decide that you do not want a file to be included in a commit, you could unstage the file, using “git reset HEAD []”. 9. Checkout a particular version of the file To discard local changes, you could use “git checkout []”, which gives you a latest version of the file from the repository. If you would like a particular version of the file. You could do “git checkout abcde []” where ‘abcde’ is the hash of the commit that you want. 10. Revert commit To revert a particular commit, you could use “git revert”. One example usage is “git revert HEAD~3”, which revert the changes specified by the fourth last commit in HEAD and create a new commit with the reverted changes. 11. Asking for help a. $ git help or $ git help 12. Configure Git using “git config

6.170 Tutorial 1 - Git

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