git diff、git diff head、git diff --cached三者详细区分

 参考:

git diff 文件对比
git diff filepath 工作区与暂存区比较
git diff HEAD filepath 工作区与HEAD ( 当前工作分支) 比较
git diff --staged 或 --cached filepath 暂存区与HEAD比较
git diff branchName filepath 当前分支的文件与branchName 分支的文件进行比较
git diff commitId filepath 与某一次提交进行比较