shell脚本中$$等变量的含义

$$等变量在shell脚本中的含义：

#!/bin/bash

#the meaning of variables

echo "process ID: $$"
echo "current file name: $0"
echo "the number of parameters: $#"
echo "parameters list: $*"
echo "arguments list: $@"
echo "first var: $1"
echo "second var: $2"
echo "shell return state: $?"

保存为var.sh文件，运行结果：

XXX@XXX:~/scripts$ sh var.sh var1 var2 var3
process ID: 7262
current file name: var.sh
the number of parameters: 3
parameters list: var1 var2 var3
arguments list: var1 var2 var3
first var: var1
second var: var2
shell return state: 0