管理修改

Git跟蹤並管理修改，而非檔案。

做實驗驗證。第一步，對readme.txt做一個修改，比如加一行內容：

$ 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.

然後通過git add提交修改，通過git status檢視工作區狀態：

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

        modified:   readme.txt

 

然後，再修改readme.txt：

$ 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.

提交：

$ git commit -m "git tracks changes"
[master 8c299f0] git tracks changes
 1 file changed, 1 insertion(+)
 

提交後，再看看狀態：

$ git status
On branch master
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

        modified:   readme.txt
            
no changes added to commit (use "git add" and/or "git commit -a")
 

可以看出，第二次修改沒有被提交

回顧操作過程：

第一次修改 -> git add -> 第二次修改 -> git commit

Git管理的是修改，當你用git add命令後，在工作區的第一次修改被放入暫存區，準備提交，但是，在工作區的第二次修改並沒有放入暫存區，所以，git commit只負責把暫存區的修改提交了，也就是第一次的修改被提交了，第二次的修改不會被提交。

提交後，用git diff HEAD -- readme.txt命令可以檢視工作區和版本庫裡面最新版本的區別：

$ git diff HEAD -- readme.txt
diff --git a/readme.txt b/readme.txt
index db28b2c..9a8b341 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.
\ No newline at end of file
+Git tracks changes of files.
\ No newline at end of file

可見，第二次修改確實沒有被提交。

小結

每次修改，如果不用git add到暫存區，那就不會加入到commit中。