Multi-dimensional arrays in Bash

Solution 1:

Bash does not support multidimensional arrays, nor hashes, and it seems that you want a hash that values are arrays. This solution is not very beautiful, a solution with an xml file should be better :

array=('d1=(v1 v2 v3)' 'd2=(v1 v2 v3)')
for elt in "${array[@]}";do eval $elt;done
echo "d1 ${#d1[@]} ${d1[@]}"
echo "d2 ${#d2[@]} ${d2[@]}"

EDIT: this answer is quite old, since since bash 4 supports hash tables, see also this answer for a solution without eval.

Solution 2:

Bash doesn't have multi-dimensional array. But you can simulate a somewhat similar effect with associative arrays. The following is an example of associative array pretending to be used as multi-dimensional array:

declare -A arr
arr[0,0]=0
arr[0,1]=1
arr[1,0]=2
arr[1,1]=3
echo "${arr[0,0]} ${arr[0,1]}" # will print 0 1

If you don't declare the array as associative (with -A), the above won't work. For example, if you omit the declare -A arr line, the echo will print 2 3 instead of 0 1, because 0,0, 1,0 and such will be taken as arithmetic expression and evaluated to 0 (the value to the right of the comma operator).

Solution 3:

This works thanks to 1. "indirect expansion" with ! which adds one layer of indirection, and 2. "substring expansion" which behaves differently with arrays and can be used to "slice" them as described https://stackoverflow.com/a/1336245/317623

# Define each array and then add it to the main one
SUB_0=("name0" "value 0")
SUB_1=("name1" "value;1")
MAIN_ARRAY=(
  SUB_0[@]
  SUB_1[@]
)

# Loop and print it.  Using offset and length to extract values
COUNT=${#MAIN_ARRAY[@]}
for ((i=0; i<$COUNT; i++))
do
  NAME=${!MAIN_ARRAY[i]:0:1}
  VALUE=${!MAIN_ARRAY[i]:1:1}
  echo "NAME ${NAME}"
  echo "VALUE ${VALUE}"
done

It's based off of this answer here

Solution 4:

If you want to use a bash script and keep it easy to read recommend putting the data in structured JSON, and then use lightweight tool jq in your bash command to iterate through the array. For example with the following dataset:

[

    {"specialId":"123",
    "specialName":"First"},

    {"specialId":"456",
    "specialName":"Second"},

    {"specialId":"789",
    "specialName":"Third"}
]

You can iterate through this data with a bash script and jq like this:

function loopOverArray(){

    jq -c '.[]' testing.json | while read i; do
        # Do stuff here
        echo "$i"
    done
}

loopOverArray

Outputs:

{"specialId":"123","specialName":"First"}
{"specialId":"456","specialName":"Second"}
{"specialId":"789","specialName":"Third"}

Solution 5:

Independent of the shell being used (sh, ksh, bash, ...) the following approach works pretty well for n-dimensional arrays (the sample covers a 2-dimensional array).

In the sample the line-separator (1st dimension) is the space character. For introducing a field separator (2nd dimension) the standard unix tool tr is used. Additional separators for additional dimensions can be used in the same way.

Of course the performance of this approach is not very well, but if performance is not a criteria this approach is quite generic and can solve many problems:

array2d="1.1:1.2:1.3 2.1:2.2 3.1:3.2:3.3:3.4"

function process2ndDimension {
    for dimension2 in $*
    do
        echo -n $dimension2 "   "
    done
    echo
}

function process1stDimension {
    for dimension1 in $array2d
    do
        process2ndDimension `echo $dimension1 | tr : " "`
    done
}

process1stDimension

The output of that sample looks like this:

1.1     1.2     1.3     
2.1     2.2     
3.1     3.2     3.3     3.4