在Shell脚本中读取矩阵中的值

Question

 # reading into array
 for(( i=0;i<2;i++)) do
     for((j=0;j<2;j++)) do
         read a[i][j]        
     done
 done

 # printing 
 for(( i=0;i<2;i++)) do
     for((j=0;j<2;j++) do
         echo -n ${a[i][j]}" "
     done
     echo  
 done

When we read the values in matrix

2 3
4 5

it assigns only the values 3 5 and prints

3 3
5 5

Answer 1

You can simulate 2D arrays with index arithmetic in a couple of ways. Here is a common method:

#!/bin/bash

## read values into a 1D array using nested loops and
## simulated 2D addressing
for ((i = 0; i < 2; i++)); do
    for ((j = 0; j < 2; j++)); do
        read a[$((i * 2 + j))]
    done
done

## Output the values contained in a simulated 2D manner
for ((i = 0; i < 2; i++)); do
    for ((j = 0; j < 2; j++)); do
        printf " %2d" ${a[$((i * 2 + j))]}
    done
    echo ""
done

Output

$ bash sim2darray.sh
1
2
3
4
  1  2
  3  4

With a few additional bits of formatting you can make a nice looking simulated 2D array:

#!/bin/bash

for ((i = 0; i < 5; i++)); do
    for ((j = 0; j < 5; j++)); do
        a[$((i * 5 + j))]=$((i * 5 + j))
    done
done

printf "\nThe simulated 5x5 2D array:\n\n"
for ((i = 0; i < 5; i++)); do
    [ "$i" -eq 0 ] && printf "[[" || printf " ["

    for ((j = 0; j < 5; j++)); do
        printf " %3d" ${a[$((i * 5 + j))]}
    done

    [ "$i" -eq 4 ] && printf " ]]\n\n" || printf " ]\n"
done

Example Use/Output

$ bash sim2darray.sh

The simulated 5x5 2D array:

[[   0   1   2   3   4 ]
 [   5   6   7   8   9 ]
 [  10  11  12  13  14 ]
 [  15  16  17  18  19 ]
 [  20  21  22  23  24 ]]