Git SCM Tutorial

เนื้อหา

1 How To Use the GitLab
2 Git SCM Turotial
3 ขั้นตอนการเรียนรู้
4 git commit
5 สรุปการทำงานคำสั่งของ GitSCM
- 5.1 การสร้างโครงการ

How To Use the GitLab

Conclusion

Git SCM Turotial

Git เป็นเครื่องมือที่ได้รับความนิยม ซึ่งมีเครื่องมือหลายอย่างมาช่วยในการทำงาน เช่น Github.com, Gitlab เป็นต้น

ขั้นตอนการเรียนรู้

เข้าไปที่ http://gitref.org/ เพื่อพิมพ์ตาม และสังเกตแต่ละคำสั่งว่าทำงานอย่างไร

git init

initializes a directory as a Git repository

$ cd konnichiwa
$ ls
 README   hello.rb

This is a project where we are writing examples of the "Hello World" program in every language. So far, we just have Ruby, but hey, it's a start. To start version controlling this with Git, we can simply run git init.

$ git init
 Initialized empty Git repository in /opt/konnichiwa/.git/

Now you can see that there is a .git subdirectory in your project. This is your Git repository where all the data of your project snapshots are stored.

$ ls -a
 .        ..       .git     README   hello.rb

Congratulations, you now have a skeleton Git repository and can start snapshotting your project.

In a nutshell, you use git init to make an existing directory of content into a new Git repository. You can do this in any directory at any time, completely locally.

git clone

copy a git repository so you can add to it

If you need to collaborate with someone on a project, or if you want to get a copy of a project so you can look at or use the code, you will clone it. You simply run the git clone [url] command with the URL of the project you want to copy.

$ git clone git://github.com/schacon/simplegit.git
 Initialized empty Git repository in /private/tmp/simplegit/.git/
 remote: Counting objects: 100, done.
 remote: Compressing objects: 100% (86/86), done.
 remote: Total 100 (delta 35), reused 0 (delta 0)
 Receiving objects: 100% (100/100), 9.51 KiB, done.
 Resolving deltas: 100% (35/35), done.
 $ cd simplegit/
 $ ls
 README   Rakefile lib

This will copy the entire history of that project so you have it locally and it will give you a working directory of the main branch of that project so you can look at the code or start editing it. If you change into the new directory, you can see the .git subdirectory - that is where all the project data is.

$ ls -a
 .        ..       .git     README   Rakefile lib
 $ cd .git
 $ ls
 HEAD        description info        packed-refs
 branches    hooks       logs        refs
 config      index       objects

By default, Git will create a directory that is the same name as the project in the URL you give it - basically whatever is after the last slash of the URL. If you want something different, you can just put it at the end of the command, after the URL.

In a nutshell, you use git clone to get a local copy of a Git repository so you can look at it or start modifying it.

Basic Snapshotting

In a nutshell, you will use git add to start tracking new files and also to stage changes to already tracked files, then git status and git diff to see what has been modified and staged and finally git commit to record your snapshot into your history. This will be the basic workflow that you use most of the time.

git add

Going back to our Hello World example, once we've initiated the project, we would now start adding our files to it and we would do that with git add. We can use git status to see what the state of our project is.

$ git status -s  
 ?? README
 ?? hello.rb

So right now we have two untracked files. We can now add them.

$ git add README hello.rb

Now if we run git status again, we'll see that they've been added.

$ git status -s
 A  README
 A  hello.rb

It is also common to recursively add all files in a new project by specifying the current working directory like this: git add .. Since Git will recursively add all files under a directory you give it, if you give it the current working directory, it will simply start tracking every file there. In this case, a git add . would have done the same thing as a git add README hello.rb , or for that matter so would git add *, but that's only because we don't have subdirectories which the * would not recurse into.

OK, so now if we edit one of these files and run git status again, we will see something odd.

$ vim README
$ git status -s
 AM README
 A  hello.rb

The 'AM' status means that the file has been modified on disk since we last added it. This means that if we commit our snapshot right now, we will be recording the version of the file when we last ran git add, not the version that is on our disk. Git does not assume that what the file looks like on disk is necessarily what you want to snapshot - you have to tell Git with the git add command.

In a nutshell, you run git add on a file when you want to include whatever changes you've made to it in your next commit snapshot. Anything you've changed that is not added will not be included - this means you can craft your snapshots with a bit more precision than most other SCM systems.

For a very interesting example of using this flexibility to stage only parts of modified files at a time, see the '-p' option to git add in the Pro Git book.

git status

view the status of your files in the working directory and staging area

As you saw in the git add section, in order to see what the status of your staging area is compared to the code in your working directory, you can run the git status command. Using the -s option will give you short output. Without that flag, the git status command will give you more context and hints. Here is the same status output with and without the -s. The short output looks like this:

$ git status -s
 AM README
 A  hello.rb

Where the same status with the long output looks like this:

$ git status
 # On branch master
 #
 # Initial commit
 #
 # Changes to be committed:
 #   (use "git rm --cached <file>..." to unstage)
 #
 # new file:   README
 # new file:   hello.rb
 #
 # Changed but not updated:
 #   (use "git add <file>..." to update what will be committed)
 #   (use "git checkout -- <file>..." to discard changes in working directory)
 #
 # modified:   README
 #

You can easily see how much more compact the short output is, but the long output has useful tips and hints as to what commands you may want to use next.

Git will also tell you about files that were deleted since your last commit or files that were modified or staged since your last commit.

$ git status -s
 M  README
 D hello.rb

You can see there are two columns in the short status output. The first column is for the staging area, the second is for the working directory. So for example, if you have the README file staged and then you modify it again without running git add a second time, you'll see this:

$ git status -s
 MM README
 D hello.rb

In a nutshell, you run git status to see if anything has been modified and/or staged since your last commit so you can decide if you want to commit a new snapshot and what will be recorded in it.

git diff shows diff of what is staged and what is modified but unstaged

There are two main uses of the git diff command. One use we will describe here, the other we will describe later in the "Inspection and Comparison" section. The way we're going to use it here is to describe the changes that are staged or modified on disk but unstaged. git diff show diff of unstaged changes

Without any extra arguments, a simple git diff will display in unified diff format (a patch) what code or content you've changed in your project since the last commit that are not yet staged for the next commit snapshot.

$ vim hello.rb
$ git status -s
 M hello.rb
$ git diff
 diff --git a/hello.rb b/hello.rb
 index d62ac43..8d15d50 100644
 --- a/hello.rb
 +++ b/hello.rb
 @@ -1,7 +1,7 @@
 class HelloWorld
  def self.hello
 -    puts "hello world"
 +    puts "hola mundo"
  end
 end

So where git status will show you what files have changed and/or been staged since your last commit, git diff will show you what those changes actually are, line by line. It's generally a good follow-up command to git status git diff --cached show diff of staged changes

The git diff --cached command will show you what contents have been staged. That is, this will show you the changes that will currently go into the next commit snapshot. So, if you were to stage the change to hello.rb in the example above, git diff by itself won't show you any output because it will only show you what is not yet staged.

$ git status -s
 M hello.rb
$ git add hello.rb 
$ git status -s
 M  hello.rb
$ git diff
$

If you want to see the staged changes, you can run git diff --cached instead.

$ git status -s
 M  hello.rb
$ git diff
$ 
$ git diff --cached
 diff --git a/hello.rb b/hello.rb
 index d62ac43..8d15d50 100644
 --- a/hello.rb
 +++ b/hello.rb
 @@ -1,7 +1,7 @@
 class HelloWorld
  def self.hello
 -    puts "hello world"
 +    puts "hola mundo"
  end
 end

git diff HEAD show diff of all staged or unstaged changes

If you want to see both staged and unstaged changes together, you can run git diff HEAD - this basically means you want to see the difference between your working directory and the last commit, ignoring the staging area. If we make another change to our hello.rb file then we'll have some changes staged and some changes unstaged. Here are what all three diff commands will show you:

$ vim hello.rb 
$ git diff
 diff --git a/hello.rb b/hello.rb
 index 4f40006..2ae9ba4 100644
 --- a/hello.rb
 +++ b/hello.rb
 @@ -1,7 +1,7 @@
 class HelloWorld
 +  # says hello
 def self.hello
    puts "hola mundo"
   end
 end
$ git diff --cached
 diff --git a/hello.rb b/hello.rb
 index 2aabb6e..4f40006 100644
 --- a/hello.rb
 +++ b/hello.rb
 @@ -1,7 +1,7 @@
 class HelloWorld
 def self.hello
 -    puts "hello world"
 +    puts "hola mundo"
  end
 end
$ git diff HEAD
 diff --git a/hello.rb b/hello.rb
 index 2aabb6e..2ae9ba4 100644
 --- a/hello.rb
 +++ b/hello.rb
 @@ -1,7 +1,8 @@
 class HelloWorld
 +  # says hello
 def self.hello
 -    puts "hello world"
 +    puts "hola mundo"
  end
 end

git diff --stat show summary of changes instead of a full diff

If we don't want the full diff output, but we want more than the git status output, we can use the --stat option, which will give us a summary of changes instead. Here is the same example as above, but using the --stat option instead.

$ git status -s
 MM hello.rb
$ git diff --stat
 hello.rb |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
$ git diff --cached --stat
 hello.rb |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
$ git diff HEAD --stat
 hello.rb |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

You can also provide a file path at the end of any of these options to limit the diff output to a specific file or subdirectory.

In a nutshell, you run git diff to see details of the git status command - how files have been modified or staged on a line by line basis.

git commit

records a snapshot of the staging area

Now that you have staged the content you want to snapshot with the git add command, you run git commit to actually record the snapshot. Git records your name and email address with every commit you make, so the first step is to tell Git what these are.

$ git config --global user.name 'Your Name'
$ git config --global user.email you@somedomain.com

Let's stage and commit all the changes to our hello.rb file. In this first example, we'll use the -m option to provide the commit message on the command line.

$ git add hello.rb 
$ git status -s
 M  hello.rb
$ git commit -m 'my hola mundo changes'
 [master 68aa034] my hola mundo changes
 1 files changed, 2 insertions(+), 1 deletions(-)

Now we have recorded the snapshot. If we run git status again, we will see that we have a "clean working directory", which means that we have not made any changes since our last commit - there is no un-snapshotted work in our checkout.

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

If you leave off the -m option, Git will try to open a text editor for you to write your commit message. In vim, which it will default to if it can find nothing else in your settings, the screen might look something like this:

 # Please enter the commit message for your changes. Lines starting
 # with '#' will be ignored, and an empty message aborts the commit.
 # On branch master
 # Changes to be committed:
 #   (use "git reset HEAD <file>..." to unstage)
 #
 # modified:   hello.rb
 #
 ~
 ~
 ".git/COMMIT_EDITMSG" 9L, 257C

At this point you add your actual commit message at the top of the document. Any lines starting with '#' will be ignored - Git will put the output of the git status command in there for you as a reminder of what you have modified and staged.

In general, it's very important to write a good commit message. For open source projects, it's generally a rule to write your message more or less in this format:

Short (50 chars or less) summary of changes

More detailed explanatory text, if necessary. Wrap it to about 72 characters or so. In some contexts, the first line is treated as the subject of an email and the rest of the text as the body. The blank line separating the summary from the body is critical (unless you omit the body entirely); some git tools can get confused if you run the two together.

Further paragraphs come after blank lines.

 - Bullet points are okay, too
 - Typically a hyphen or asterisk is used for the bullet, preceded by a
  single space, with blank lines in between, but conventions vary
  here
 # Please enter the commit message for your changes. Lines starting
 # with '#' will be ignored, and an empty message aborts the commit.
 # On branch master
 # Changes to be committed:
 #   (use "git reset HEAD <file>..." to unstage)
 #
 # modified:   hello.rb
 #
 ~
 ~
 ~
 ".git/COMMIT_EDITMSG" 25L, 884C written

The commit message is very important. Since much of the power of Git is this flexibility in carefully crafting commits locally and then sharing them later, it is very powerful to be able to write three or four commits of logically separate changes so that your work may be more easily peer reviewed. Since there is a separation between committing and pushing those changes, do take the time to make it easier for the people you are working with to see what you've done by putting each logically separate change in a separate commit with a nice commit message so it is easier for them to see what you are doing and why.

git commit -a automatically stage all tracked, modified files before the commit

If you think the git add stage of the workflow is too cumbersome, Git allows you to skip that part with the -a option. This basically tells Git to run git add on any file that is "tracked" - that is, any file that was in your last commit and has been modified. This allows you to do a more Subversion style workflow if you want, simply editing files and then running git commit -a when you want to snapshot everything that has been changed. You still need to run git add to start tracking new files, though, just like Subversion.

$ vim hello.rb
$ git status -s
 M  hello.rb
$ git commit -m 'changes to hello file'
 # On branch master
 # Changed but not updated:
 #   (use "git add <file>..." to update what will be committed)
 #   (use "git checkout -- <file>..." to discard changes in working directory)
 #
 # modified:   hello.rb
 #
 no changes added to commit (use "git add" and/or "git commit -a")
$ git commit -am 'changes to hello file'
 [master 78b2670] changes to hello file
 1 files changed, 2 insertions(+), 1 deletions(-)

Notice how if you don't stage any changes and then run git commit, Git will simply give you the output of the git status command, reminding you that nothing is staged. The important part of that message has been highlighted, saying that nothing is added to be committed. If you use -a, it will add and commit everything at once.

This now lets you complete the entire snapshotting workflow - you make changes to your files, then use git add to stage files you want to change, git status and git diff to see what you've changed, and then finally git commit to actually record the snapshot forever.

In a nutshell, you run git commit to record the snapshot of your staged content. This snapshot can then be compared, shared and reverted to if you need to.

สรุปการทำงานคำสั่งของ GitSCM

การสร้างโครงการ

init
clone

การทำงานพื้นฐานโดยสรุป

add
status
diff
commit
reset
rm, mv
stash

การแตกสาขา Brach และการรวม Merge

branch
checkout
merge
log
tag

การแบ่งปันและปรับปรุงโครงการ

fetch, pull
push
remote

การตรวจตราและเปรียบเทียบ

log
diff