git tutorial learning Notes (2)

git tutorials to learn from Liao Xuefeng's official website

1. version rollback

Modify readme.txt file submitted to the Git repository, for example:

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

Any modified several versions add and commit later, consider the change to the current version has been for generations?

In practice, the mind how we might remember a few thousand lines of each file have changed what, or to do version control system. Version control system must have a command history can tell us, in Git, we git logview the command

$ git log
commit e82e6f6c8b90fbf95f23273e7c7a37973529d463 (HEAD -> master)
Author: leox <leox520@163.com>
Date:   Wed Sep 4 15:21:19 2019 +0800

    append HAHAHA

commit cf418a19d4725b02680b08b83414cea9bb0c797b
Author: leox <leox520@163.com>
Date:   Wed Sep 4 15:18:46 2019 +0800

    append GPL

commit 7f6805e527555bc4a2d153a6e85ec86a2661f2f2
Author: leox <leox520@163 .com> 
a Date: Wed On Sep . 4  14 : 52 is : 31 is  2019 + 0800 

    adds a txt file

git logCommand to display the most recent commit log from the farthest we can see the 3 submission, most recently append HAHAHA, the last time add GPL, the earliest of which was added a txt file.

If the output too much information, see dazzling, you can try to add --pretty=onelineparameters:

Git log $ - Pretty = oneline 
e82e6f6c8b90fbf95f23273e7c7a37973529d463 (the HEAD -> Master) the append HAHAHA 
cf418a19d4725b02680b08b83414cea9bb0c797b the append the GPL 
7f6805e527555bc4a2d153a6e85ec86a2661f2f2 added a txt file

Tips required is that you see the long list of similar e82e6f6c8b ...is commit id(version number), and not the same as SVN, Git is commit idnot 1,2,3 ...... incremental number, but a SHA1 calculated from a very large digital, hexadecimal, and you see commit id, and I certainly do not like to your subject. Why commit idwe need to use such strings of numbers that represent it? Because Git is a distributed version control system, we have to study people back to work in the same repository, if everyone uses 1,2,3 ...... as the version number, it is certainly on the conflict.

Well, now we start Time Machine, ready to readme.txtfall back to the previous version, is add GPLthat version, how to do it?

First of all, Git must know the current version of which version, in Git, use HEADrepresents the current version, which is the latest submitted e82e6f6c8b ...(note my submission ID and you are certainly not the same), the previous version is HEAD^, the previous version is HEAD^^, of course, up 100 write 100 version ^is easier to count, so written HEAD~100.

Now, we want the current version append HAHAHAto fall back to the previous version add GPL, you can use git resetthe command:

$ git reset --hard HEAD^
HEAD is now at cf418a1 append GPL

Now and then to see the readme.txt file, it really is restored.

You can continue to fall back to the previous version wrote a readme file, but wait a minute, and then we git loglook at the current state of the repository:

Git log $ 
the commit cf418a19d4725b02680b08b83414cea9bb0c797b (the HEAD -> Master) 
the Author: LEOX <leox520 @ 163 .com> 
a Date: Wed On Sep . 4  15 : 18 is : 46 is  2019 + 0800 

    the append the GPL 

the commit 7f6805e527555bc4a2d153a6e85ec86a2661f2f2 
the Author: LEOX <leox520 @ 163 .com> 
a Date: Sep Wed 4  14 : 52 : 31  2019 + 0800 

    added a txt file

The latest version that append GPLhas been to see! You sit like Time Machine from the 21 century came in the 19th century, already want to go back and go back, swollen do?

Way but it is still there, as long as the above command line window has not been turned off, you can follow up ah searched and searched to find that append HAHAHAthe commit idis e82e6f6c8b9 ..., so he can return to specify a future version:

$ git reset --hard e82e6
HEAD is now at e82e6f6 append HAHAHA

And then view the readme.txt file, HAHAHA is back! !

$ cat readme.txt
Git is a distributed  version control system. sound HAHAHA.
Git is free software distributed under the GPL.

Git version rollback speed is very fast, because Git inside there is a point to the current version of the HEADpointer when you roll back version of the time, Git is just from the HEAD points append GPL:

┌────┐
│　HEAD  │
└────┘
   │
   └──> ○ append GPL
        │
        ○ add distributed
        │
        ○ wrote a readme file

To point to add distributed:

┌────┐
│  HEAD　│
└────┘
   │
   │    ○ append GPL
   │    │
   └──> ○ add distributed
        │
        ○ wrote a readme file

Then the way to update the document workspace. So you get HEADpoints which version number, you put the current version of the positioning is.

Now, you fall back to a version, turn off the computer, you'll regret it the next morning, and would like to return to a new version of how to do? Can not find the new version of commit idhow to do?

In Git, there is always regret it can eat. When you use $ git reset --hard HEAD^retreated back to the add HAHAHAtime of release, would like to return to append GPL, you must find append GPLthe commit id. Git provides a command git reflogto record your every command:

$ git reflog
e82e6f6 (HEAD -> master) HEAD@{0}: reset: moving to e82e6
cf418a1 HEAD@{1}: reset: moving to HEAD^
e82e6f6 (HEAD -> master) HEAD@{2}: commit: append HAHAHA
cf418a1 HEAD@{3}: commit: append GPL
7f6805e HEAD@{4}: commit (initial): 添加了一个txt文件

Finally sigh, we can see from the output, append GPLthe commit id is cf418a1 , now, and you can ride a time machine back to the future.