Fill a bash array from a NUL separated input - arrays

Question

I want to create a bash array from a NUL separated input (from stdin).
Here's an example:
## Let define this for clarity
$ hd() { hexdump -v -e '/1 "%02X "'; echo ;}
$ echo -en "A B\0C\nD\0E\0" | hd
41 20 42 00 43 0A 44 00 45 00
So this is my input.
Now, working with NUL works fine if not using the -a of read command:
$ while read -r -d '' v; do echo -n "$v" | hd; done < <(echo -en "A B\0C\nD\0E\0")
41 20 42
43 0A 44
45
We get the correct values. But I can't store these values using -a:
$ read -r -d '' -a arr < <(echo -en "A B\0C\nD\0E\0")
$ declare -p arr
declare -a arr='([0]="A" [1]="B")'
Which is obviously not what I wanted. I would like to have:
$ declare -p arr
declare -a arr='([0]="A B" [1]="C
D" [2]="E")'
Is there a way to go with read -a, and if it doesn't work, why? Do you know a simple way to do this (avoiding the while loop) ?

Answer 1

read -a is the wrong tool for the job, as you've noticed; it only supports non-NUL delimiters. The appropriate technique is given in BashFAQ #1:
arr=()
while IFS= read -r -d '' entry; do
arr+=( "$entry" )
done
In terms of why read -d '' -a is the wrong tool: -d gives read an argument to use to determine when to stop reading entirely, rather than when to stop reading a single element.
Consider:
while IFS=$'\t' read -d $'\n' words; do
...
done
...this will read words separated by tab characters, until it reaches a newline. Thus, even with read -a, using -d '' will read until it reaches a NUL.
What you want, to read until no more content is available and split by NULs, is not a '-d' of NUL, but no end-of-line character at all (and an empty IFS). This is not something read's usage currently makes available.

Answer 2

bash-4.4-alpha added a -d option to mapfile:
The `mapfile' builtin now has a -d option to use an arbitrary
character
as the record delimiter, and a -t option to strip the delimiter as
supplied with -d.
— https://tiswww.case.edu/php/chet/bash/CHANGES
Using this, we can simply write:
mapfile -t -d '' arr < <(echo -en "A B\0C\nD\0E\0")

Answer 3

If anyone wonders, here's the function (using while) that I use to store values from a NUL-separated stdin:
read_array () {
local i
var="$1"
i=0
while read -r -d '' value; do
printf -v "$var[$i]" "%s" "$value"
i=$[$i + 1]
done
}
It can then be used quite cleanly:
$ read_array arr < <(echo -en "A B\0C\nD\0E\0")
$ declare -p arr
declare -a arr='([0]="A B" [1]="C
D" [2]="E")'

Answer 4

Here's a simplification of #vaab's function. It uses bash 4.3's nameref feature:
read_array () {
local -n a=$1
while read -r -d '' value; do
a+=("$value")
done
}
Test:
test_it () {
local -a arr
read_array arr < <(echo -en "A B\0C\nD\0E\0")
declare -p arr
}
test_it