path: root/git.html.markdown

---
category: tool
tool: git
contributors:
    - ["Jake Prather", "http://github.com/JakeHP"]
filename: LearnGit.txt
---

Git is a distributed version control and source code management system. 

It does this through a series of snapshots of your project, and it works 
with those snapshots to provide you with functionality to version and 
manage your source code.

## Versioning Concepts

### What is version control?

Version control is a system that records changes to a file, or set of files, over time.

### Centralized Versioning VS Distributed Versioning

* Centralized version control focuses on synchronizing, tracking, and backing up files.
* Distributed version control focuses on sharing changes. Every change has a unique id.
* Distributed systems have no defined structure. You could easily have a SVN style, 		centralized system, with git.

[Additional Information](http://git-scm.com/book/en/Getting-Started-About-Version-Control)

### Why Use Git?

* Can work offline.
* Collaborating with others is easy!
* Branching is easy!
* Merging is easy!
* Git is fast.
* Git is flexible.

## Git Architecture


### Repository

A set of files, directories, historical records, commits, and heads. Imagine it as a source code data structure,
with the attribute that each source code "element" gives you access to its revision history, among other things.

A git repository is comprised of the .git directory & working tree.

### .git Directory (component of repository)

The .git directory contains all the configurations, logs, branches, HEAD, and more.
[Detailed List.](http://gitready.com/advanced/2009/03/23/whats-inside-your-git-directory.html)

### Working Tree (component of repository)

This is basically the directories and files in your repository. It is often referred to
as your working directory.

### Index (component of .git dir)

The Index is the staging area in git. It's basically a layer that separates your working tree
from the Git repository. This gives developers more power over what gets sent to the Git
repository.

### Commit

A git commit is a snapshot of a set of changes, or manipulations to your Working Tree.
For example, if you added 5 files, and removed 2 others, these changes will be contained
in a commit (or snapshot). This commit can then be pushed to other repositories, or not!

### Branch

A branch is essentially a pointer that points to the last commit you made. As you commit,
this pointer will automatically update and point to the latest commit.

### HEAD and head (component of .git dir)

HEAD is a pointer that points to the current branch. A repository only has 1 *active* HEAD.
head is a pointer that points to any commit. A repository can have any number of heads.

### Conceptual Resources

* [Git For Computer Scientists](http://eagain.net/articles/git-for-computer-scientists/)
* [Git For Designers](http://hoth.entp.com/output/git_for_designers.html)


## Commands


### init

Create an empty Git repository. The Git repository's settings, stored information, 
and more is stored in a directory (a folder) named ".git".

```bash
$ git init
```

### config

To configure settings. Whether it be for the repository, the system itself, or global
configurations.


```bash
# Print & Set Some Basic Config Variables (Global)
$ git config --global user.email
$ git config --global user.name

$ git config --global user.email "MyEmail@Zoho.com"
$ git config --global user.name "My Name"
```

[Learn More About git config.](http://git-scm.com/docs/git-config)

### help

To give you quick access to an extremely detailed guide of each command. Or to
just give you a quick reminder of some semantics.

```bash
# Quickly check available commands
$ git help

# Check all available commands
$ git help -a

# Command specific help - user manual
# git help <command_here>
$ git help add
$ git help commit
$ git help init
```

### status

To show differences between the index file (basically your working copy/repo) and the current
HEAD commit.


```bash
# Will display the branch, untracked files, changes and other differences
$ git status

# To learn other "tid bits" about git status
$ git help status
```

### add

To add files to the current working tree/directory/repo. If you do not `git add` new files to the
working tree/directory, they will not be included in commits!

```bash
# add a file in your current working directory
$ git add HelloWorld.java

# add a file in a nested dir
$ git add /path/to/file/HelloWorld.c

# Regular Expression support!
$ git add ./*.java
```

### branch

Manage your branches. You can view, edit, create, delete branches using this command.

```bash
# list existing branches & remotes
$ git branch -a

# create a new branch
$ git branch myNewBranch

# delete a branch
$ git branch -d myBranch

# rename a branch
# git branch -m <oldname> <newname>
$ git branch -m myBranchName myNewBranchName

# edit a branch's description
$ git branch myBranchName --edit-description
```

### checkout

Updates all files in the working tree to match the version in the index, or specified tree.

```bash
# Checkout a repo - defaults to master branch
$ git checkout
# Checkout a specified branch
$ git checkout branchName
# Create a new branch & switch to it, like: "git branch <name>; git checkout <name>"
$ git checkout -b newBranch
```

### clone

Clones, or copies, an existing repository into a new directory. It also adds
remote-tracking branches for each branch in the cloned repo, which allows you to push
to a remote branch.

```bash
# Clone learnxinyminutes-docs
$ git clone https://github.com/adambard/learnxinyminutes-docs.git
```

### commit

Stores the current contents of the index in a new "commit." This commit contains
the changes made and a message created by the user.

```bash
# commit with a message
$ git commit -m "Added multiplyNumbers() function to HelloWorld.c"
```

### diff

Shows differences between a file in the working directory, index and commits.

```bash
# Show difference between your working dir and the index
$ git diff

# Show differences between the index and the most recent commit.
$ git diff --cached

# Show differences between your working dir and the most recent commit
$ git diff HEAD
```

### grep

Allows you to quickly search a repository.

Optional Configurations:

```bash
# Thanks to Travis Jeffery for these
# Set line numbers to be shown in grep search results
$ git config --global grep.lineNumber true

# Make search results more readable, including grouping
$ git config --global alias.g "grep --break --heading --line-number"
```

```bash
# Search for "variableName" in all java files
$ git grep 'variableName' -- '*.java'

# Search for a line that contains "arrayListName" and, "add" or "remove"
$ git grep -e 'arrayListName' --and \( -e add -e remove \) 
```

Google is your friend; for more examples
[Git Grep Ninja](http://travisjeffery.com/b/2012/02/search-a-git-repo-like-a-ninja)

### log

Display commits to the repository.

```bash
# Show all commits
$ git log

# Show X number of commits
$ git log -n 10

# Show merge commits only
$ git log --merges
```

### merge

"Merge" in changes from external commits into the current branch.

```bash
# Merge the specified branch into the current.
$ git merge branchName

# Always generate a merge commit when merging
$ git merge --no-ff branchName
```

### mv

Rename or move a file	

```bash
# Renaming a file
$ git mv HelloWorld.c HelloNewWorld.c

# Moving a file
$ git mv HelloWorld.c ./new/path/HelloWorld.c

# Force rename or move
# "existingFile" already exists in the directory, will be overwritten
$ git mv -f myFile existingFile
```

### pull

Pulls from a repository and merges it with another branch.

```bash
# Update your local repo, by merging in new changes
# from the remote "origin" and "master" branch.
# git pull <remote> <branch>
# git pull => implicitly defaults to => git pull origin master
$ git pull origin master

# Merge in changes from remote branch and rebase
# branch commits onto your local repo, like: "git pull <remote> <branch>, git rebase <branch>"
$ git pull origin master --rebase
```

### push

Push and merge changes from a branch to a remote & branch.

```bash
# Push and merge changes from a local repo to a 
# remote named "origin" and "master" branch.
# git push <remote> <branch>
# git push => implicitly defaults to => git push origin master
$ git push origin master

# To link up current local branch with a remote branch, add -u flag:
$ git push -u origin master
# Now, anytime you want to push from that same local branch, use shortcut:
$ git push 
```

### stash

Stashing takes the dirty state of your working directory and saves it on a
stack of unfinished changes that you can reapply at any time.

```bash
# Let's say you've been doing some work in your git repo, but you want to pull from the remote.
# Since you have dirty (uncommited) changes to some files, you are not able to run 'git pull'.
# Instead, you can run 'git stash' to save your changes onto a stack!

$ git stash
Saved working directory and index state \
  "WIP on master: 049d078 added the index file"
  HEAD is now at 049d078 added the index file
  (To restore them type "git stash apply") 

# Now you can pull!
git pull
# ...changes apply...

# Now check that everything is OK

$ git status
# On branch master
nothing to commit, working directory clean

# You can see what 'hunks' you've stashed so far:
# Since the 'hunks' are stored in a Last-In-First-Out stack
# our most recent change will be at top
$ git stash list
stash@{0}: WIP on master: 049d078 added the index file
stash@{1}: WIP on master: c264051 Revert "added file_size"
stash@{2}: WIP on master: 21d80a5 added number to log

# Now let's apply our dirty changes back by popping them off the stack
# 'git stash apply' also works too
$ git stash pop
# On branch master
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#
#      modified:   index.html
#      modified:   lib/simplegit.rb
#

# Now you're good to go!

[Additional Reading.](http://git-scm.com/book/en/v1/Git-Tools-Stashing)

### rebase (caution) 

Take all changes that were committed on one branch, and replay them onto another branch.
*Do not rebase commits that you have pushed to a public repo*.

```bash
# Rebase experimentBranch onto master
# git rebase <basebranch> <topicbranch>
$ git rebase master experimentBranch
```

[Additional Reading.](http://git-scm.com/book/en/Git-Branching-Rebasing)

### reset (caution)

Reset the current HEAD to the specified state. This allows you to undo merges,
pulls, commits, adds, and more. It's a great command but also dangerous if you don't
know what you are doing.

```bash
# Reset the staging area, to match the latest commit (leaves dir unchanged)
$ git reset

# Reset the staging area, to match the latest commit, and overwrite working dir
$ git reset --hard

# Moves the current branch tip to the specified commit (leaves dir unchanged)
# all changes still exist in the directory.
$ git reset 31f2bb1

# Moves the current branch tip backward to the specified commit
# and makes the working dir match (deletes uncommited changes and all commits
# after the specified commit).
$ git reset --hard 31f2bb1
```

### rm

The opposite of git add, git rm removes files from the current working tree.

```bash
# remove HelloWorld.c
$ git rm HelloWorld.c

# Remove a file from a nested dir
$ git rm /pather/to/the/file/HelloWorld.c
```

## Further Information

* [tryGit - A fun interactive way to learn Git.](http://try.github.io/levels/1/challenges/1)

* [git-scm - Video Tutorials](http://git-scm.com/videos)

* [git-scm - Documentation](http://git-scm.com/docs)

* [Atlassian Git - Tutorials & Workflows](https://www.atlassian.com/git/)

* [SalesForce Cheat Sheet](https://na1.salesforce.com/help/doc/en/salesforce_git_developer_cheatsheet.pdf)

* [GitGuys](http://www.gitguys.com/)

* [Git - the simple guide](http://rogerdudler.github.io/git-guide/index.html)