Introduction to shell-related directives

$#, the number of arguments followed by the script runtime

#! /bin/bash

Case ' $# ' in
   0) printf "Enter A number:  "
      Read
      n= $REPLY
       ;;
    *) n=$1
       ;;
Esac
X=$ (((1 + $n) * $n/2))
echo "Tne value of 1 + 2 + 3....+ $n = $x"

The meaning of this shell:
If the number of arguments is zero, you are prompted to enter a number;
If the number of arguments is nonzero, the value of the first parameter is taken
Then calculate the value of 1 to this number, output!

Echo >> is append, echo > is overlay


$* and [email protected] and $ #的区别

For example,
The script name is called test.sh Three: 1 2 3
After running test.sh 1 2 3
$* is "1 2 3" (enclosed in quotation marks)
[Email protected] is "1" "2" "3" (separately wrapped)
$ #为3 (number of parameters)

Introduction to shell-related directives