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