Git Crash Course (deprecated)

Posted on | In |

Author: @x1aokeHuang

Date: Apr. 28th 2019

# deprecated

Please move to the new Chinese version.

Introduction to Git

  • Git is a fast, simple and popular distributed version control system (VCS).
  • This is how it was born, somehow sounds very chivalrous:
    1. Linus build the open-source Linux, but its version control is so bad that Linus had to receive all the source code via e-mails from volunteers all over the world!
    2. Then in 2002 a commercial company called BitMover offered their VCS software BitKeeper to Linux community.
    3. For some members in the community wanted to crack the protocol of BitKeepers, BitMover had to get back the free license.
    4. Linus spent 2 weeks writing a CVS from nothing using C programming language. After a month, the source code of Linux was managed by the newly created Git. Git ends up with a huge success in VCS software.

Centralization vs. Distribution

  • Centralization:

    version repository is in the central server. Users has to fetch files from the server, and commit to it after modifying the files.

  • Distribution:

    Each users own a full copy of the files. In reality, we commit files to a so called “central server” to make file-exchanging convenient.

Install Git

  • Depends on the platform you use

Build Repository

  • Initialize a repo:

    Open git bash!

    Firstly, build a empty directory:

    1
    2
    3
    4
    $ mkdir learngit
    $ cd learngit
    $ pwd
    /Users/michael/learngit

    Then use git init:

    1
    2
    $ git init
    Initialized empty Git repository in /Users/michael/learngit/.git/

    PS: Don’t modify the files in .git

  • Add files to repo:

    make a file under current path like “readme.txt”.

    1. Use git add to add file(s):

      1
      $ git add readme.txt

    2. Use git commit commit file(s) to repo:

      1
      2
      3
      4
      $ git commit -m "wrote a readme file"
      [master (root-commit) eaadf4e] wrote a readme file
       1 file changed, 2 insertions(+)
       create mode 100644 readme.txt

    PS:

    1. You can add several files at a time before you commit.
    2. Encoding setting: UTF-8 without BOM.

Git: A Time Travel Machine

Modify Files:

  • Change readme.txt:

    1
    2
    Git is a distributed version control system.
    Git is free software.

  • Run git status:

    1
    2
    3
    4
    5
    6
    7
    8
    9
    $ git status
    On branch master
    Changes not staged for commit:
      (use "git add ..." to update what will be committed)
      (use "git checkout -- ..." to discard changes in working directory)

        modified:   readme.txt

    no changes added to commit (use "git add" and/or "git commit -a")

    It shows current status of the repo, telling us that readme.txt has been modified but not been commit yet.

  • Run git diff:

    1
    2
    3
    4
    5
    6
    7
    8
    9
    $ git diff readme.txt 
    diff --git a/readme.txt b/readme.txt
    index 46d49bf..9247db6 100644
    --- a/readme.txt
    +++ b/readme.txt
    @@ -1,2 +1,2 @@
    -Git is a version control system.
    +Git is a distributed version control system.
     Git is free software.

    git diff means difference, and its format is from Unix diff.

    After knowing what has been changed, we can commit file at ease.

  • Then we add file, git status to make sure the file we want to commit, finally we commit and final check:

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    $ git add readme.txt

    $ git status
    On branch master
    Changes to be committed:
      (use "git reset HEAD ..." to unstage)

        modified:   readme.txt

    $ git commit -m "add distributed"
    [master e475afc] add distributed
     1 file changed, 1 insertion(+), 1 deletion(-)

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

    Summary:

    1. git status shows current status of the repo.
    2. if git status shows there is a change in files, use git diff to see what’s going on.

Version Rolling Back: