inode包含文件的元信息，具体来说有以下内容：
文件的字节数
文件拥有者的User ID
文件的Group ID
文件的读、写、执行权限
文件的时间戳，共有三个：ctime指inode上一次变动的时间，mtime指文件内容上一次变动的时间，atime指文件上一次打开的时间。
链接数，即有多少文件名指向这个inode
文件数据block的位置
可以用stat命令，查看某个文件的inode信息：
stat example.txt

#!/bin/sh
myFile="/root/apue/example.xml"
if [ ! -f "$myFile" ]; then
    cp  ./example.xml  /root/apue/
fi

-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.