Skip to content

Latest commit

 

History

History
279 lines (185 loc) · 7.36 KB

Readme.md

File metadata and controls

279 lines (185 loc) · 7.36 KB
Raw

Up To Schedule - Back To Write Code for People - Forward to Don't Repeat Yourself

Make Incremental Changes I: Use Version Control

Based on materials by Katy Huff, Anthony Scopatz, Joshua R. Smith, Sri Hari Krishna Narayanan, and Matthew Gidden

Motivation

See motivation.pdf.

Introduction

We will cover git (and GitHub) in several sessions. There exist numerous graphical user interfaces for git (including GitHub for Mac and GitHub for Windows), but we will focus on using git from the command-line in the bash shell.

Initial setup: git config

We first need to setup git with our user name and email address, and tell it what editor we use. The last command tells git to provided output in color.

$ git config --global user.name "YOUR NAME"
$ git config --global user.email "YOUR EMAIL"
$ git config --global core.editor nano
$ git config --global color.ui true

These commands modify the file ~/.gitconfig. Type less ~/.gitconfig to see what it did.

Create a local repository: git init

A git repository is a directory on your computer. You will use git to track the files and subdirectories in that directory. To begin to use git to track a directory, you must first initialize the repository with git init.

Starting from scratch, you first create a directory for your repository, change to that directory, and type git init.

Exercise Exercise: Create a Local Repository

Initialize your repository: change to your home directory, create a new directory, change to that directory, and type git init.

$ cd
$ mkdir simplestats
$ cd simplestats
$ git init
Initialized empty Git repository in /Users/swc/simplestats/.git/

A .git subdirectory is created; git will store all of its material (configuration information and the entire history) here.

$ ls -A
.git
$ ls -A .git
HEAD        config      description hooks       info        objects     refs

Routine use of git

You use git init just once for a project, to initialize the git repository.

Day-to-day, the basic use of git is the following:

  • Change some files
  • See what you've changed, with git status, git diff, and git log.
  • Indicate what changes to save, with git add.
  • Commit to those changes, with git commit.

Check the status of your repository: git status

Use git status to check the current status of things in your repository

$ git status
On branch master

Initial commit

nothing to commit (create/copy files and use "git add" to track)

This says that nothing much is going on. We will talk about branches later.

Adding a File To Version Control: git add

You need to specify which files within the directory you would like to keep track of. To do so, you must add them to the repository with git add. But first you need to create a file.

Typically the first file to add would be a ReadMe file describing the project. This can be a plain text file or a Markdown file (with the .md extension). Markdown is simple system for adding some light mark-up, like bold and italics, to indicate sections, and hyperlinks.

Exercise Exercise: Add a File to Your Local Repository

Step 1: Create a file to add to your repository.

$ cd ~/simplestats/
$ touch README.md

Step 2: Add some text to the file.

$ nano README.md

Step 3: Use git status to check the status of the repository.

$ git status

Step 4: Tell git that you want to keep track of this file.

$ git add README.md

Step 5: Check the status again.

$ git status

Commit your changes: git commit

Committing changes to your repository involves two steps: indicating the changes to be committed with git add (known as "staging the changes", which we have just done), and then actually committing those changes with git commit.

If you type just git commit, an editor will open for you to add a comment describing the changes. Alternatively, use can use the -m flag followed by the comment in quotes.

Exercise Exercise: Commit Your Changes

Step 1: Commit the file you just added to your repository.

$ git commit -m "This is the first commit. It adds a readme file."

Step 2: Admire your work.

$ git status

ADVICE: Commit often

In the same way that it is wise to often save a document that you are working on, so too is it wise to save numerous revisions of your code. More frequent commits increase the granularity of your undo button.

ADVICE: Good commit messages

There are no hard and fast rules, but good commits are atomic: they are the smallest change that remain meaningful. A good commit message usually contains a one-line overview followed by a longer explanation if necessary.

The repository for this course has some good commit messages.

Viewing the differences: git diff

git diff is similiar to the shell command diff, but rather than comparing two files, it is used to show the historical changes in a repository.

If you type git diff alone, it will show all changes in your working directory that have not yet been staged for a commit.

Exercise Exercise: Try git diff

Step 1: Try out git diff without having made any changes

$ git diff

Step 2: Make a change to the README.md file.

$ nano README.md

Step 3: Use git diff to view the changes.

$ git diff

A summarized version of this output can be output with the --stat flag:

$ git diff --stat

To see only the differences in a certain file or subdirectory, use git diff [path]. For example:

$ git diff README.md

To see the changes that are staged for commit, use

$ git diff --cached

Exercise Exercise: Use git diff with staged changes

Step 1: Stage the change you made to README.md.

$ git add README.md

Step 2: Try git diff on its own.

$ git diff

Step 3: Use git diff to see the staged changes.

$ git diff --cached

Step 4: Commit your change

$ git commit -m "Small change to README.md"

Viewing the history: git log

A log of the commit messages is kept by the repository and can be reviewed with the log command.

$ git log
commit 1863aefd7db752f58226264e5f4282bda641ddb3
Author: Joshua Smith <joshua.r.smith@gmail.com>
Date:   Wed Feb 8 16:08:08 2012 -0600

    This is the first commit. It adds a readme file.

There are some useful flags for this command, such as

-p
-3
--stat
--oneline
--graph
--pretty=short/full/fuller/oneline
--since=X.minutes/hours/days/weeks/months/years or YY-MM-DD-HH:MM
--until=X.minutes/hours/days/weeks/months/years or YY-MM-DD-HH:MM
--author=<pattern>

Resources

Up To Schedule - Back To Write Code for People - Forward to Don't Repeat Yourself