git format-patch 生成指定commit的補丁

官方解釋：
The first rule takes precedence in the case of a single . To apply the second rule, i.e., format everything since the beginning of history up until , use the --root option: git format-patch --root . If you want to format only itself, you can do this with git format-patch -1 commit .

git format經常使用命令：
git format-patch -3 //從當前分支最新提交點往下共生成3個補丁
git format-patch -1 指定commit號 //生成指定commit號的補丁
eg：git format-patch -1 5f123e379cc97c317d6094bcfa2281e1189d61f3
生成5f123e379cc97c317d6094bcfa2281e1189d61f3號的補丁，該commit號不必定在該分支開頭，能夠在該分支的任意位置。
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