Shell's $

1. $$: The process ID representing the shell script

2. $!: The process ID representing the last executed shell script

3. $?: Represents the return value of the last executed shell command

4. $*: Represents all parameters in the form "parameter one parameter two parameter three"

5. [Email protected]: Also represents all parameters, the format is "parameter one" "parameter two" "Parameter three"

6. $: Represents the name of the shell script

7. $ $n: Represents the input parameter

8. $#: Represents the number of output parameters
   

Shell's $