[SOLVED] Bash: filling 2d Array - strange behaviour

Issue

At first I declare an array with declare -a matrix and do not initialize any values. Then I print the values of the array in the following way: if a value of the matrix on the particular position equals 1 it should print 1, else it should print _

So without setting any values I get the predictable output.

But if I for example do: matrix[10,10]=1 and I print the array, suddenly always on the position matrix[x,10] the value is always 1.

Why does it behave like this? What do I have to do if I only want to initialize some particular positions with 1 and not all the others in the same row?

#!/bin/bash
#read N
declare -a matrix

for (( i=0; i<10; i++));do
    for (( j=0; j<20; j++));do
        if [[ matrix[$i,$j] -eq 1 ]];then
            printf 1
        else
            printf _
        fi
    done
    echo
done

echo

matrix[10,10]=1

for (( i=0; i<10; i++));do
    for (( j=0; j<20; j++));do
        if [[ matrix[$i,$j] -eq 1 ]];then
            printf 1
        else
            printf _
        fi
    done
    echo
done

thats the output:

____________________
____________________
____________________
____________________
____________________
____________________
____________________
____________________
____________________
____________________

__________1_________
__________1_________
__________1_________
__________1_________
__________1_________
__________1_________
__________1_________
__________1_________
__________1_________
__________1_________

Solution

There are no 2D arrays in Bash.

The stuff inside [..] is arithmetically evaluated. , there is a comma operator. The result is the second value. matrix[10,10]=1 is the same as matrix[1,2,3,4,5,etc,10]=1 is the same as matrix[10]=1.

You can use associative arrays, in which case the stuff inside [...] is a string, in which case , will be a character. declare -A matrix. Note that your loop (( i=0; i<10; i++)) never goes to 10.

Answered By - KamilCuk

Answer Checked By - Gilberto Lyons (WPSolving Admin)