shell判断文件是否存在，我们真的明白了吗？

Unix Korn Shell Scripting Reference Sheet中的一段，关于判断文件是否存在等相关的一些问题
(pdf文件在这里可以下载到：
http://blogimg.chinaunix.net/blog/upfile2/090707170244.pdf)

Conditional Logic on Files

-a file exists.
-b file exists and is a block special file.
-c file exists and is a character special file.
-d file exists and is a directory.
-e file exists (just the same as -a).
-f file exists and is a regular file.
-g file exists and has its setgid(2) bit set.
-G file exists and has the same group ID as this process.
-k file exists and has its sticky bit set.
-L file exists and is a symbolic link.
-n string length is not zero.
-o Named option is set on.
-O file exists and is owned by the user ID of this process.
-p file exists and is a first in, first out (FIFO) special file or
named pipe.
-r file exists and is readable by the current process.
-s file exists and has a size greater than zero.
-S file exists and is a socket.
-t file descriptor number fildes is open and associated with a
terminal device.
-u file exists and has its setuid(2) bit set.
-w file exists and is writable by the current process.
-x file exists and is executable by the current process.
-z string length is zero.

是用 -s 还是用 -f 这个区别是很大的！
写shell脚本还是要非常慎重的，很多地方都可能是问题的隐患！