How to return an array in bash without using globals?

With Bash version 4.3 and above, you can make use of a nameref so that the caller can pass in the array name and the callee can use a nameref to populate the named array, indirectly.

#!/usr/bin/env bash

create_array() {
    local -n arr=$1             # use nameref for indirection
    arr=(one "two three" four)
}

use_array() {
    local my_array
    create_array my_array       # call function to populate the array
    echo "inside use_array"
    declare -p my_array         # test the array
}

use_array                       # call the main function

Produces the output:

inside use_array
declare -a my_array=([0]="one" [1]="two three" [2]="four")

You could make the function update an existing array as well:

update_array() {
    local -n arr=$1             # use nameref for indirection
    arr+=("two three" four)     # update the array
}

use_array() {
    local my_array=(one)
    update_array my_array       # call function to update the array
}

This is a more elegant and efficient approach since we don’t need command substitution $() to grab the standard output of the function being called. It also helps if the function were to return more than one output – we can simply use as many namerefs as the number of outputs.

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Here is what the Bash Manual says about nameref:

A variable can be assigned the nameref attribute using the -n option
to the declare or local builtin commands (see Bash Builtins) to create
a nameref, or a reference to another variable. This allows variables
to be manipulated indirectly. Whenever the nameref variable is
referenced, assigned to, unset, or has its attributes modified (other
than using or changing the nameref attribute itself), the operation is
actually performed on the variable specified by the nameref variable’s
value. A nameref is commonly used within shell functions to refer to a
variable whose name is passed as an argument to the function. For
instance, if a variable name is passed to a shell function as its
first argument, running

declare -n ref=$1 inside the function creates a nameref variable ref
whose value is the variable name passed as the first argument.
References and assignments to ref, and changes to its attributes, are
treated as references, assignments, and attribute modifications to the
variable whose name was passed as $1.