直接执行 git diff
减号代表旧文件,加号代表新文件存放在工作区
git diff 快照ID 快照ID
git diff HEAD 比较最新提交的快照和工作目录
git diff 快照ID 比较指定快照和工作目录
git diff --cached 比较暂存区和最新提交的文件
git diff --cached 快照ID 比较暂存区和指定快照文件