Basic use of Git version rollback and Git log and Git reset –hard commit_id

Version back

• Now that you’ve learned how to modify files and commit your changes to Git repositories, try again and modify the readme.txt file as follows:

Git is a distributed version control system.
Git is free software distributed under the GPL.
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• Then try to submit:

$ git add readme.txt
$ git commit -m "append GPL"
[master 1094adb] append GPL
 1 file changed, 1 insertion(+), 1 deletion(-)
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• Like this, you’re constantly making changes to the file and then committing changes to the repository, just like in an RPG where every level you pass is automatically saved, and if you fail to pass a level, you can choose to read the state of the previous level. Sometimes, before a Boss fight, you’ll manually save the game so you can pick up from the nearest place if the Boss fight fails. Git is the same way. Whenever you feel your files have changed enough, you can”Save a snapshotThis snapshot is called in Gitcommit. If you make a mess or delete a file by mistake, you can always go to the nearest onecommitRecover and get back to work instead of losing months of work.
• Now, let’s reviewreadme.txtThere are several versions of files that have been committed to the Git repository:
• Version 1:wrote a readme file

Git is a version control system.
Git is free software.
Copy the code

• Version 2:add distributed

Git is a distributed version control system.
Git is free software.
Copy the code

• Version 3:append GPL

Git is a distributed version control system.
Git is free software distributed under the GPL.
Copy the code

• In practice, of course, it’s impossible to remember in your head what a document with thousands of lines has changed every time, otherwise you wouldn’t need a version control system. There must be some command in the version control system that tells us the history. In Git, we usegit logCommand view:

$ git logCommit 73396987016561 fb394bc3372a207c113ce42d7f (HEAD - > master) Author: user name < email > Date: Sat Aug 1 09:55:28 2020 + 0800 append the GPL commit 4 ee7803fd43a88438d6c24c308e74f5e2625e25e Author: user name < email > Date: Sat Aug 1 09:46:49 2020 + 0800 add distributed commit three f0724615d7e891dc9626491a3467657edfa3e89 Author: user name < email > Date: Sat Aug 1 09:38:45 2020 +0800 wrote a readme fileCopy the code

The git log command displays the latest and most recent commit logs. You can see three commits: append GPL, Add Distributed, and Wrote a Readme file.

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

$ git log --pretty=oneline
73396987016561fb394bc3372a207c113ce42d7f (HEAD -> master) append GPL
4ee7803fd43a88438d6c24c308e74f5e2625e25e add distributed
3f0724615d7e891dc9626491a3467657edfa3e89 wrote a readme file
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• And just as a reminder, you see a bunch of similar things7339698… isCommit ID (version number)Unlike SVN, Gitcommit idnotOne, two, three...Increasing numbers, but oneSHA1A very large number calculated withhexadecimalAnd what you seecommit idIt’s not the same as mine. Yours will prevail. whycommit idWhy do I have to use this big string of numbers?Because Git is a distributed version control system, we will have to study how many people work in the same version library. If everyone uses 1,2,3… As a version number, that’s definitely a conflict.
• Every time you commit a new version, Git actually strings them together into an automatic timeline. If you use a visual tool to view Git history, you can see the timeline of commit history more clearly:

• All right, now let’s fire up the time machine and get ready toreadme.txtGo back to the previous version, which isadd distributedHow do you do that?
• First, Git must know which version is currently available. In Git, useHEADRepresents the current version, which is the latest commit7339698… (Note that my submission ID is definitely different from yours), the previous version wasHEAD^The previous version wasHEAD^^Of course up100A version of the writing100个^It’s a little bit harder to count, so let’s write itHEAD~100.
• Now, we’re going to put the current versionappend GPLRollback to the previous versionadd distributed, can be usedgit resetCommand:

$ git reset --hard HEAD^
HEAD is now at 4ee7803 add distributed
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What is the value of the hard parameter? I’ll talk about that later, but for now, you can use it safely.

• Take a look atreadme.txtThe content is not versionadd distributed:

$ cat readme.txt
Git is a distributed version control system.
Git is free software.
Copy the code

It was restored.

• You can continue to roll back to the previous versionwrote a readme fileBut wait, let’s use itgit logTake a look at the current state of the repository:

$ git logCommit 4 ee7803fd43a88438d6c24c308e74f5e2625e25e (HEAD - > master) Author: user name < email > Date: Sat Aug 1 09:46:49 2020 + 0800 add distributed commit three f0724615d7e891dc9626491a3467657edfa3e89 Author: user name < email > Date: Sat Aug 1 09:38:45 2020 +0800 wrote a readme fileCopy the code

• The latest editionappend GPLIt’s gone!It’s like you took a time shuttle from the 21st century to the 19th century, and you can’t go back. What do you do?
• There is a way, as long as the command line window above is still open, you can just go up and up and down and find itappend GPLthecommit idis7339698..., so you can specify a future version:

$ git reset --hard 73396
HEAD is now at 7339698 append GPL
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• It is not necessary to write the full version number, just the first few digits will do, Git will automatically find it. Of course, you can’t just write the first one or two, because Git may find multiple version numbers and never know which one it is.
• And look carefullyreadme.txtContent:

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

Sure enough, the version went back to the third revision of the version content.

• Git version rollback is very fast because Git has an internal reference to the current versionHEADThe pointer, when you roll back the version, Git is just a pointerHEADFrom the point toappend GPL:

┌ ─ ─ ─ ─ ┐ │ HEAD │ └ ─ ─ ─ ─ ┘ │ └ ─ ─ > a. a. add distributed append the GPL │ │ demonstrate a readme fileCopy the code

• To point toadd distributed:

┌ ─ ─ ─ ─ ┐ │ HEAD │ └ ─ ─ ─ ─ ┘ │ │.through append the GPL │ │ └ ─ ─ >.through the add distributed │ demonstrate a readme fileCopy the code

• I also updated the files in the workspace. So you getHEADWhatever version number you point to, you locate the current version.
• Now, what if you fall back to a version, turn it off, regret it the next morning, and want to go back to the new version? Can’t find the new versioncommit idHow to do?
• In Git, there is always a remedy for regret. When you use$ git reset --hard HEAD^Back to theadd distributedVersion, then want to restore toappend GPLYou have to find itAppend Commit ID of the GPL. Git provides a commandgit reflogTo record every command you make:

$ git reflog
7339698 (HEAD -> master) HEAD@{0}: reset: moving to 73396
4ee7803 HEAD@{1}: reset: moving to HEAD^
7339698 (HEAD -> master) HEAD@{2}: commit: append GPL
4ee7803 HEAD@{3}: commit: add distributed
3f07246 HEAD@{4}: commit (initial): wrote a readme file
Copy the code

• Finally, a sigh of relief, and from the output,Append Commit ID of the GPLis7339698Now you can travel back to the future in a time machine.

summary