[Review at the end of Linux] (Nine-nine and nine multiplication table, output * triangle)

                                                  Final review

1. Investigation of internal variables

Internal variable	Explanation
$0	The file name of the current script
$n	The parameters passed to the script or function. n is a number, indicating the first few parameters. For example, the first parameter is $ 1, the second parameter is $ 2, and so on
$#	Number of parameters passed to script or function
$*	All parameters passed to the script or function
$@	All parameters passed to the script or function.
$?	The exit status of the last command, or the return value of the function
$$	Current Shell process ID. For shell scripts, this is the process ID where these scripts are located

 

2. Shell programming 

(1) Nine nine multiplication table

#！/bin/bash
for((i=1;i<=9;i++)) 
do
    for((j=1;j<=i;j++))
    do
    echo -n -e "$j*$i="$[j*i]" "
    done
echo -e ""
done

 The output is 

1*1=1

1*2=2 2*2=4

1*3=3 2*3=6 3*3=9

1*4=4 2*4=8 3*4=12 4*4=16

1*5=5 2*5=10 3*5=15 4*5=20 5*5=25

1*6=6 2*6=12 3*6=18 4*6=24 5*6=30 6*6=36

1*7=7 2*7=14 3*7=21 4*7=28 5*7=35 6*7=42 7*7=49

1*8=8 2*8=16 3*8=24 4*8=32 5*8=40 6*8=48 7*8=56 8*8=64

1*9=9 2*9=18 3*9=27 4*9=36 5*9=45 6*9=54 7*9=63 8*9=72 9*9=81

(2) Output * triangle