git add -u：将文件的修改、文件的删除，添加到暂存区。

git add .：将文件的修改，文件的新建，添加到暂存区。

git add -A：将文件的修改，文件的删除，文件的新建，添加到暂存区。

本地有改动（包括删除和修改）的已经追踪的文件

       -u, --update
           Update the index just where it already has an entry matching
           <pathspec>. This removes as well as modifies index entries to match
           the working tree, but adds no new files.


           If no <pathspec> is given when -u option is used, all tracked files
           in the entire working tree are updated (old versions of Git used to
           limit the update to the current directory and its subdirectories).

-A

       -A, --all, --no-ignore-removal
           Update the index not only where the working tree has a file
           matching <pathspec> but also where the index already has an entry.
           This adds, modifies, and removes index entries to match the working
           tree.


           If no <pathspec> is given when -A option is used, all files in the
           entire working tree are updated (old versions of Git used to limit
           the update to the current directory and its subdirectories).

1.  git add -A   保存所有的修改

2.  git add .     保存新的添加和修改，但是不包括删除

3.  git add -u   保存修改和删除，但是不包括新建文件。

如图：