what's wrong with my programming?

[hhdong12_cassie]

Hi,
I am a beginner of the shell script programming. I tried to print out a 4 *4 (black and white) chessboard on my screen, but it doesn't work. my programming is :

************************************************** *********
$ vi chessboard.sh
# using for-loop to print out a chessboard on screen
for((i=1;i<5;i++))
do
for((j=1;j<5;j++))
do
sum=`expr $i + $j`
index=`expr $sum % 2`
if [ $index -eq 0 ]; then
echo -e -n "\033[47m"
else
echo -e -n "\033[40m"
fi
done
echo -e -n "\033[47m" #set background to grey#
echo " "
done
************************************************** *********

my screen background is white, but it seems there is no command to set the white color ( i used "echo -e
"\033[47m", but it is grey background).

I don't know what's wrong with the above programming, it just doesn't give me a normal chessboard! : (

can anyone help me to fix it? thanks in advance!

[jozyba]

echo -n " " - your screen is white by default so this line should print two white spaces.
echo -e -n "\033[40m \033[0m" - this line sets the background to black, prints two black spaces, then resets all atributes to their default (white background)

#! /bin/bash

for((i=1;i<5;i++)); do
    for((j=1;j<5;j++)); do
        sum=$(expr $i + $j)
        index=$(expr $sum &#37; 2)
        if [ $index -eq 0 ]; then
            echo -n "  "
        else
            echo -e -n "\033[40m  \033[0m"
        fi
    done
    echo
done

And if you wanted to put a grey border around the board you could do it like this:

#! /bin/bash

GREY_LN="\033[47m                    \033[0m"
GREY_SQ="\033[47m  \033[0m"
BLACK_SQ="\033[40m  \033[0m"
WHITE_SQ="  "

echo -e "$GREY_LN"
for((i=1;i<9;i++)); do
    echo -e -n "$GREY_SQ"
    for((j=1;j<9;j++)); do
        sum=$(expr $i + $j)
        index=$(expr $sum % 2)
        if [ $index -eq 0 ]; then
            echo -n "$WHITE_SQ"
        else
            echo -e -n "$BLACK_SQ"
        fi
    done
    echo -e "$GREY_SQ"
done
echo -e "$GREY_LN"

Or you could mark out the grid like so:

#! /bin/bash

number=8
GREY_LN="\033[30;47m  a b c d e f g h   \033[0m"
BLACK_SQ="\033[40m  \033[0m"
WHITE_SQ="  "

echo -e "$GREY_LN"
for((i=1;i<9;i++)); do
    echo -e -n "\033[47m${number} \033[0m"
    for((j=1;j<9;j++)); do
        sum=$(expr $i + $j)
        index=$(expr $sum % 2)
        if [ $index -eq 0 ]; then
            echo -n "$WHITE_SQ"
        else
            echo -e -n "$BLACK_SQ"
        fi
    done
    echo -e "\033[47m ${number}\033[0m"
    let "number-=1"
done
echo -e "$GREY_LN"