[SOLVED] Why can't an associative Bash array be assigned with an array?

Issue

According to man bash it is possible to assign an associative array with a flat list of key-value pairs:

[…] or a list of words that is interpreted as a sequence of alternating keys and values: name=( key1 value1 key2 value2 ...)

This does work, but it does not work to use an array to get these "alternating keys and values": name=( "${someArray[@]}" )

Consider this example:

#!/usr/bin/env bash

set -u

#declare -A map=(one ONE two TWO)
array=(one ONE two TWO)
declare -A map=("${array[@]}")
# Workaround with `eval`:
#eval "declare -A map=(${array[@]@Q})"

echo "KEYS:"
printf '    %s\n' "${!map[@]}"
echo "VALUES:"
printf '    %s\n' "${map[@]}"

echo "${#map[@]}"

Actual output:

KEYS:
    one ONE two TWO
VALUES:
    

Expected output:

KEYS:
    two
    one
VALUES:
    TWO
    ONE

Why is that so?

Solution

Include the array parens in the quoted string to preserve the whitespace between items for the declaration. Also, if keys or values themselves contain whitespace, use @Q to quote each item:

array=(one 'O NE' 'tw o' TWO)
declare -A map="(${array[@]@Q})"

echo "KEYS:"
printf '    %s\n' "${!map[@]}"
echo "VALUES:"
printf '    %s\n' "${map[@]}"

echo "${#map[@]}"

KEYS:
    one
    tw o
VALUES:
    O NE
    TWO
2

Tested with GNU bash 5.2.21

Answered By - pmf

Answer Checked By - Katrina (WPSolving Volunteer)