Learning notes: [$*],[$@] and [$#] in a shell script [$?] [$] [$] [$] [$!] ... What do you mean, separately?

For example, the
script name is called test.sh Three: 1 2 3 is as follows

./test.sh 1 2 3  

After running test.sh 1 2 3

$* is "1 2 3" (enclosed in quotes)
$@ is "1" "2" "3" (wrapped separately)
$ #为3 (number of parameters)

Case 2:

#!/bin/bash 
My_fun () { 
    echo "$#" 
} 
Echo ' The number of parameter in ' $@ ' is ' $ (my_fun "$@")    
Echo ' the Number of parameter in ' $* ' is ' $ (my_fun ' $* ')

Execution:./my.sh p1 "P2 P3" P4 after return:  

The number of parameter in "$@" are 3      //"$@" = "P1" "P2 P3" "P4" the number of

parameter in "$*" is 1     //"$*" = "P1 P2 p3 P4"

$n
The first parameter is represented, and the second parameter is $ ...

$#
Number of command line arguments

$
The name of the current program

$?
The return code of the previous command or function

$*
With the parameter 1 parameter 2 ... Save all parameters in the form

$@
With the parameter 1″ parameter 2″ ... Save all parameters in the form

$
PID for this program (process ID number)

$!
PID of the previous command