# Git Book
[Git Book](https://git-scm.com/book/en/v2)

## Chapter 1
* Git tracks snapshots, not differences (virtual filesystem)
* Nearly every operation is local
* Has integrity included
* Generally only adds data

### Three states
| Working Directory | Staging area | .git repository |
|------------------:|:------------:|:----------------|
|    <=             | = checkout=  | =<              |
| stage >=          | =>           |                 |
|                   | commit >=    | =>              |

### First time setup
* Global: /etc/gitconfig
* Per-user: .gitconfig
* Per-project: .git/config

```
$ git config --global user.name "John Doe"
$ git config --global user.email johndoe@example.com
$ git config --global core.editor vim
$ git config --list
```

### Get help
* git help 'verb'
* git 'verb' --help
* man git-'verb'

## Chapter 2

### Getting a Repository
* New repositor: `$ git init`
* Clone existing: `$ git clone https://github.com/libgit2/libgit2 [mygitlib]`

### Reordering Changes
| Untracked | Unmodified | Modified | Staged |
|----------:|:----------:|:--------:|:-------|
| add the file >= | ==   |  ==      | =>     |
|           | edit the file >= | => |        |
|           |            | stage the file >= | => |
| <=        | =< remove the file |  |        |
|           | <=         | ==       | =< commit the file |

* Checking the status:
  `$ git status`
* Adding file(s)
  `$ git add .`
  `$ git add README.md`
  `$ git add *.c`
* Staging modified files
  `$ git add modified.file`
* The same file can be staged and unstaged, if it was edited after staging!
* Short status
  `git status -s`
  - Left letter: status of the staging area
  - Right letter: status of the working tree
  - ??: untracked
  - A : added to the staging area
  - MM: modified, staged, modified again
  -  M: modified, not yet staged
  - M : modified and staged
* ignore files over .gitignore Examples:
  - `*.a`: no a-files...
  - `!lib.a`: ...except for lib.a
  - `/TODO`: ignore TODO in the current directory, but not in other directories
  - `build/`: ignore all files in the build directory
  - `doc/*.txt`: ignore txt files in the doc directory
  - `doc/**/*.pdf`: ignore txt files in doc and all its subdirs

### View staged and unstaged changes
* See unstaged changes:
  `$ git diff`
* See staged changed:
  `$ git diff --staged` or `$ git diff --cached`

### Committing your changes
* Commit staged files: `$ git commit` or `$ got commit -m "my message"`
* Skip the staging area: `$ git commit -a -m "my message"`
  - it's equivalent to `git add .` followed by `$ git commit -m "my message"`

### Removing files
* `$ git rm` removes files from the _staging_ area and removes it from the drive.
* if you first remove a file with `$ rm` the change will be recorded. You must still type `$ git rm` to remove it from the stage area before committing.
* if you modified a file and already added it to the staging area, you must use -f to force the removal. This is a security feature, because the data couldn't be recovered by git.
* You can remove files from the staging area but keep it on the drive (e.g. if you forgot to put them in .gitignore).
  `$ git rm --cached`

### Moving files
* Git is smart about file moves. therefore the two options are equivalent:
  - `$ git mv a b`
  - `$ mv a b` followed by `$ git rm a && git add b`

### Viewing the history
* Generally with `$ git log`
* show diffs of changes and limit to last N entries: `$ git log -p -N`
* show abbreviated stats: `$ git log --stat`
* use --pretty=keyword option. Keywords are
  - oneline
  - short
  - full
  - fuller
  - format
  ```
  $ git log --pretty=format:"%h - %an, %ar : %s"
  %H, %h:   Commit hash, abbrev. commit hash
  %T, %t:   Tree hash, abbrev. tree hash
  %P, %p:   Parent hash, abbrev. parent hash
  %an, %ae: Author name, author email
  %ad, %ar: Author date, author date, relative
  %cn, %ce: Committer name, committer email
  %cd, %cr: Committer date, committer date, relative
  %s:       Subject
  ```
* Show graph: `git log --pretty=format:"%h %s" --graph`
* other options:
  - -(n)  show only the last n commits
  - --since, --after Limit to commits after a date
  - --until, --before Limit to commits before a date
  - --author Filter by author
  - --committer Filter by committer
  - --grep Filter by content of the commit string
  - -S Only show commits adding or removing code matching the string