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今天为大家分享一篇对shell中常见参数及判断命令介绍，具有很好的参考价值。

Shell常用特殊变量

经常会在shell命令中，看到$0, $#, $*, $@, $?, $$这样的取值，这些代表什么呢？

变量	含义
$0	当前脚本的文件名
$n	传递给脚本或函数的参数。n 是一个数字，表示第几个参数。例如，第一个参数是$1，第二个参数是$2
$#	传递给脚本或函数的参数个数
$*	传递给脚本或函数的所有参数
$@	传递给脚本或函数的所有参数。被双引号(” “)包含时，与 $* 稍有不同
$?	上个命令的退出状态，或函数的返回值。成功返回0，失败返回1
$$	当前Shell进程ID。对于 Shell 脚本，就是这些脚本所在的进程ID

$* 和 $@ 都是将参数一个一个返回

"$*"将所有参数当做一个整体字符串返回 , "$@"将参数一个一个返回

常用判断参数

在shell命令文件中还经常会看到类似与if [ -z "${SPARK_HOME}" ]; then这样的判断语句？是不是也和我一样很疑惑-z是什么含义？

下面是几个常见的参数，供查询使用：

-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.