shell脚本学习

Posted 2021-12-08 zyanrong

Shell常用特殊变量

经常会在shell命令中，看到$0, $#, $*, [email protected], $?, $$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
[email protected]	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 [email protected] 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 , "[email protected]"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？例如-z是什么意思？

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.

判断命令

 shell中除了有上边这样用来判断文件是否存在的参数，当然还有判断两个数是否相等这样更常规的命令

例如，if [ $# -gt 0 ]这样判断传入参数个数是否为0

命令　　 含义
-eq 　　等于
-ne 　　不等于
-gt 　　大于
-lt 　　 小于
ge 　　大于等于
le 　　小于等于