shell脚本中 if 判断时候-s是什么意思

-s file　　　　　文件大小非0时为真
[ -f "somefile" ] ：判断是否是一个文件

[ -x "/bin/ls" ] ：判断/bin/ls是否存在并有可执行权限

[ -n "$var" ] ：判断$var变量是否有值

[ "$a" = "$b" ] ：判断$a和$b是否相等 

-r file　　　　　用户可读为真

-w file　　　　　用户可写为真

-x file　　　　　用户可执行为真

-f file　　　　　文件为正规文件为真

-d file　　　　　文件为目录为真

-c file　　　　　文件为字符特殊文件为真

-b file　　　　　文件为块特殊文件为真

-s file　　　　　文件大小非0时为真　　　　-s file true if the file has nonzero size

-t file　　　　　当文件描述符(默认为1)指定的设备为终端时为真

-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.