linux中shell变量$#,$@,$0,$1,$2的含义解释

面试题

[root@centos7 ~]#vim r1.sh 
#! /bin/bash
#  ------------------------------------------
#  Filename:    r1.sh
#  ...... //省略
# ------------------------------------------
printf "The complete list is %s\n" "$$"  //Shell本身的PID（ProcessID） 
printf "The complete list is %s\n" "$!"  //Shell最后运行的后台Process的PID 
printf "The complete list is %s\n" "$?"  //最后运行的命令的结束代码（返回值）
printf "The complete list is %s\n" "$*"  //所有参数列表。如"$*"用「"」括起来的情况、以"$1 $2 … $n"的形式输出所有参数。
printf "The complete list is %s\n" "$@"  //所有参数列表。如"$@"用「"」括起来的情况、以"$1" "$2" … "$n" 的形式输出所有参数。
printf "The complete list is %s\n" "$#"  //添加到Shell的参数个数 
printf "The complete list is %s\n" "$0"  //Shell本身的文件名 
printf "The complete list is %s\n" "$1"  //添加到Shell的各参数值。$1是第1参数、$2是第2参数…。
printf "The complete list is %s\n" "$2"  //添加到Shell的各参数值。$1是第1参数、$2是第2参数…。

结果：

[root@centos7 ~]#./r1.sh 123456 QQ
The complete list is 5327
The complete list is 
The complete list is 0
The complete list is 123456 QQ
The complete list is 123456
The complete list is QQ
The complete list is 2
The complete list is ./r1.sh
The complete list is 123456
The complete list is QQ