“git add -A” 相当于 “git add .; git add -u“.
“git add .“虽然看起来像是把目录下所有文件都添加，但是其实并没有，它只会添加新建和更改过的文件。
“git add -u” 中-u代表的是update，只会记录已有文件的update，不会记录新建的文件。
“git add -A” 可以做上面两件事的.
你可以按照下面的命令去测试这些区别:

git init
echo Change me > change-me
echo Delete me > delete-me
git add change-me delete-me
git commit -m initial
echo OK >> change-me
rm delete-me
echo Add me > add-me
git status
# Changed but not updated:
#   modified:   change-me
#   deleted:    delete-me
# Untracked files:
#   add-me
git add .
git status
# Changes to be committed:
#   new file:   add-me
#   modified:   change-me
# Changed but not updated:
#   deleted:    delete-me
git reset
git add -u
git status
# Changes to be committed:
#   modified:   change-me
#   deleted:    delete-me
# Untracked files:
#   add-me
git reset
git add -A
git status
# Changes to be committed:
#   new file:   add-me
#   modified:   change-me
#   deleted:    delete-me

总结:

• git add -A?添加所有
• git add .?添加新文件和修改的文件,?不包括删除的
• git add -u?添加修改和和删除的文件,?不包括新增的