shell脚本中判断文件是否存在

之前在编写Shell脚本时，对判断文件是否存在，没有明确区分了相关的参数选项。

先看官网说明：

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.

从上述可知：

使用“-e"用于判断任何文件是否存在；

使用"-f "用于判断文件是否存在，而这个文件必须是常规文件。

常规文件包括：文件文件/二进制文件，链接文件（链接源文件存在存在）

非常规 文件包括：设备文件（/dev目录下的文件），socket文件

因此在判断/dev/目录下的文件是否存在时必须使用“-e”选项。