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) ?
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.