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。

-u就是update的意思，只会标记本地有改动（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 . This removes as well as modifies index entries to match the working tree, but adds no new files

If no 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 就是all的意思，会标记本地所有有改动（包括删除和修改）和新增的文件

-A, –all, –no-ignore-removal

Update the index not only where the working tree has a file matching but also where the index already has an entry. This adds, modifies, and removes index entries to match the working tree.

If no 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).

总结：

git add -A 提交所有变化

git add -u 提交被修改(modified)和被删除(deleted)文件，不包括新文件(new)

git add . 提交新文件(new)和被修改(modified)文件，不包括被删除(deleted)文件