shell - Need alternative to readarray/mapfile for script on older version of Bash

Question

The script is:

#!/bin/bash

# Dynamic Menu Function
createmenu () {
    select selected_option; do # in "$@" is the default
        if [ 1 -le "$REPLY" ] && [ "$REPLY" -le $(($#)) ]; then
            break;
        else
            echo "Please make a vaild selection (1-$#)."
        fi
    done
}

declare -a drives=();
# Load Menu by Line of Returned Command
mapfile -t drives < <(lsblk --nodeps -o name,serial,size | grep "sd");
# Display Menu and Prompt for Input
echo "Available Drives (Please select one):";
createmenu "${drives[@]}"
# Split Selected Option into Array and Display
drive=($(echo "${selected_option}"));
echo "Drive Id: ${drive[0]}";
echo "Serial Number: ${drive[1]}";

The older system doesn't have mapfile or readarray so I need to convert that line to some alternative that can read each line of the lsblk output into an array.

The line in question that creates the array is:

mapfile -t drives < <(lsblk --nodeps -o name,serial,size | grep "sd");

Answer 1

You can loop over your input and append to the array:

$ while IFS= read -r line; do arr+=("$line"); done < <(printf '%d
' {0..5})
$ declare -p arr
declare -a arr='([0]="0" [1]="1" [2]="2" [3]="3" [4]="4" [5]="5")'

Or, for your specific case:

while IFS= read -r line; do
    drives+=("$line")
done < <(lsblk --nodeps -o name,serial,size | grep "sd")

See the BashFAQ/001 for an excellent explanation why IFS= read -r is a good idea: it makes sure that whitespace is conserved and backslash sequences not interpreted.