GIT study notes

Modify management, cancel

Manage changes

• Why Git is better than other versions of the control system design, because Git tracks and manages changes, not files. In other words, all modifications, such as adding a line, deleting a line, or even creating a new file are considered modifications.
• Why does Git manage changes rather than files? We can do an experiment, the first step, rightreadme.txtMake a modification, such as adding a line and adding:

$ git add readme.txt 
$ git status
Located on branch master
 Changes to be submitted:
     (Use "git reset HEAD <file> ..."  To cancel temporary storage)

• Then, modifyreadme.txtAnd submit:

$ git commit -m "git tracks changes"
[master 376d9c0] git tracks changes
 1 file changed, 1 insertion(+)

• After submission, look at the status:

$ git status
 Located on branch master
 Changes that have not been temporarily stored for submission:
     (Use "git add <file> ..."  Update the content to be submitted)
     (Use "git checkout-<file> ..."  Discard work area changes)

	 Modify: readme.txt

 Modifications have not been added for submission (use "git add"  and / or  "git commit -a"）

• we discover,The second modification was not submitted. Review the operation process:
  First modification->git add-> Second modification->git commit
• As mentioned earlier, git manages modification, when usedgit addAfter the order, the first modification in the work area is put into the temporary storage area for preparation. However, the second modification in the work area was not put into the temporary storage area, so,git commitIt is only responsible for submitting the changes in the temporary storage area, that is, the first modification is submitted, and the second modification will not be submitted.
• After submission, usegit diff HEAD -- readme.txtThe command can check the difference between the latest version in the workspace and the version library:

$ git diff HEAD -- readme.txt
diff --git a/readme.txt b/readme.txt
index 76d770f..a9c5755 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,4 +1,4 @@
 Git is a distributed version control system.
 Git is free software distributed under the GPL.
 Git has a mutable index called stage.
-Git tracks changes.
+Git tracks changes of files.

• It can be seen that the second modification was indeed not submitted.
• How can we submit the second amendment? Can continuegit addagaingit commit, Or do n’t worry about submitting the first revision, firstgit addThe second modification, and thengit commit, Which is equivalent to submitting the two amendments together.

Undo modification one

• If inreadme.txtAn extra line is added to the file, after submission, usegit statusView, Git will prompt to usegit checkout -- <file>...You can discard changes to the workspace.

$ git checkout -- readme.txt

• commandgit checkout -- readme.txtMeaning, putreadme.txtAll changes to the file in the workspace are cancelled. There are two cases:
  • One isreadme.txtIt has not been put into the temporary storage area since the modification. Now, the small modification will return to the same state as the version library;
  • One isreadme.txtAfter it has been added to the temporary storage area, changes have been made. Now, the undo changes will return to the state after being added to the temporary storage area.
• In short, it is to return this file to the most recentgit commitorgit addState at the time.
• After revocation, let's take a lookreadme.txtdocument content:

$ cat readme.txt 
Git is a distributed version control system.
Git is free software distributed under the GPL.
Git has a mutable index called stage.
Git tracks changes of files.

• File content restored
• note:git checkout -- fileIn the order--Very important, no--, It becomesSwitch to another branch, We will encounter again in the branch managementgit checkoutcommand.

Undo modification 2

• If the content to be revoked is not only written to the file, but alsogit addAdded to staging area, incommitFound this problem before, usegit statusView, the modification is just added to the temporary storage area, has not been submitted:

$ git status
 Located on branch master
 Changes to be submitted:
     (Use "git reset HEAD <file> ..."  To cancel temporary storage)

	 Modify: readme.txt

• Git also tells us that with the commandgit reset HEAD <file>You can unstage the changes in the temporary storage area and put them back in the work area.

$ git reset HEAD readme.txt
 Cancel temporary changes after reset:
M	readme.txt

• Reusegit statusCheck to make sure that the temporary storage area is clean and the work area is modified

$ git status
 Located on branch master
 Changes that have not been temporarily stored for submission:
     (Use "git add <file> ..."  Update the content to be submitted)
     (Use "git checkout-<file> ..."  Discard work area changes)

	 Modify: readme.txt

 Modifications have not been added for submission (use "git add"  and / or  "git commit -a"）

• So that we can reusecheckoutTo discard changes to the workspace.

Undo modification 3

• If the file to be modified is submitted to the repository, we will use the previous learningVersion rollback . However, this is conditional, that is, the version is rolled back before being pushed to the remote repository.

Delete Files

• In Git, deleting files is also a modification operation, let ’s add one firsttest.txtFile to Git and submit:

$ git add text.txt 
$ git commit -m "add text.txt"
[master 89274d2] add text.txt
 1 file changed, 2 insertions(+)
 create mode 100644 text.txt

• Then if we want to delete those useless files, we can delete them directly in the file manager, or usermCommand delete:

$ rm text.txt 

• At this time, Git knows that you deleted the file, so the workspace and the repository are inconsistent,git statusThe command will tell you immediately which files were deleted:

$ git status
 Located on branch master
 Changes that have not been temporarily stored for submission:
     (Use "git add / rm <file> ..."  Update the content to be submitted)
     (Use "git checkout-<file> ..."  Discard work area changes)

	 Delete: text.txt

 Modifications have not been added for submission (use "git add"  and / or  "git commit -a"）

• There are two options now, one is to actually delete the file from the repository, use the commandgit rmDelete, andgit commit：

$ git rm text.txt 
rm 'text.txt'

$ git commit -m "delete text.txt"
[master acc1af6] delete text.txt
 1 file changed, 2 deletions(-)
 delete mode 100644 text.txt

• This deletes the file from the repository.

Delete files manually before usinggit rm <file>withgit add <file>The effect is the same.

• The other case is the deletion, because there is still in the repository, so you can easily restore the accidentally deleted files to the latest version:

$ git checkout -- test.txt

• git checkoutIn fact, the version in the workspace is replaced with the version in the repository, so whether the workspace is modified or deleted, you can "one-click restore".

note: Files that have been deleted before being added to the repository cannot be recovered.