How to declare 2D array in bash

You can simulate them for example with hashes, but need care about the leading zeroes and many other things. The next demonstration works, but it is far from optimal solution.

#!/bin/bash
declare -A matrix
num_rows=4
num_columns=5

for ((i=1;i<=num_rows;i++)) do
    for ((j=1;j<=num_columns;j++)) do
        matrix[$i,$j]=$RANDOM
    done
done

f1="%$((${#num_rows}+1))s"
f2=" %9s"

printf "$f1" ''
for ((i=1;i<=num_rows;i++)) do
    printf "$f2" $i
done
echo

for ((j=1;j<=num_columns;j++)) do
    printf "$f1" $j
    for ((i=1;i<=num_rows;i++)) do
        printf "$f2" ${matrix[$i,$j]}
    done
    echo
done

the above example creates a 4×5 matrix with random numbers and print it transposed, with the example result

           1         2         3         4
 1     18006     31193     16110     23297
 2     26229     19869      1140     19837
 3      8192      2181     25512      2318
 4      3269     25516     18701      7977
 5     31775     17358      4468     30345

The principle is: Creating one associative array where the index is an string like 3,4. The benefits:

• it’s possible to use for any-dimension arrays 😉 like: 30,40,2 for 3 dimensional.
• the syntax is close to “C” like arrays ${matrix[2,3]}