在diff手册页上，我找到了这些退出值：
0 No differences were found.
1 Differences were found.
>1 An error occurred.
对于不同的错误，是否有不同的出口值高于1？
这取决于你的diff命令。 Mine(GNU diffutils 3.0)说：
An exit status of
0means no differences were found,1means some
differences were found,and2means trouble. Normally,differing
binary files count as trouble,but this can be altered by using the
-aor--textoption,or the-qor--briefoption.
