quote/escape output from local builtin to pass back to itself with builtins only?

Question

Edit: Mostly rewritten for clarity/digestibility. Also, I found one possible answer using xargs. I prefer avoiding the external command--I'll only accept my own answer if no alternative turns up.

I'm trying to pass the output of local (declared local variables as a newline-delimited key=value list), back to another invocation of local, but I'm bumping up against the edge of my understanding of bash quoting/escaping.

It's easy to handle values with no spaces, but values with internal spaces cause quoting/splitting trouble. Easier to show than tell. Using BASH_VERSION=4.4.23(1)-release. I'll walk through the steps; there's a longer repro script at the end of the post.

1. Define some local variables, and print them with the local builtin:

   function export_locals(){
       local one=1
       local two=$(echo word1 word2)
       local three=$(echo "word1 ain't word2")
       local # aka local -p
   }
   

   Which outputs some variation of:

   one=1
   three='word1 ain'\''t word2'
   two='word1 word2'
   

2. Call export_locals from another function, and pass the output to another invocation of the local builtin:

   function import_locals(){
       local $(export_locals)
       local
   }
   

   With the default IFS, this will fail. set -x shows the cause:

   + local one=1 'three='\''word1' 'ain'\''\'\'''\''t' 'word2'\''' 'two='\''word1' 'word2'\'''
   bash: local: `ain'\''t': not a valid identifier
   bash: local: `word2'': not a valid identifier
   bash: local: `word2'': not a valid identifier
   

   Using IFS=$'\n' keeps it from splitting the values of two or three, but they end up with bonus single quotes:

   + local one=1 'three='\''word1 ain'\''\'\'''\''t word2'\''' 'two='\''word1 word2'\'''
   + local
   one=1
   three=''\''word1 ain'\''\'\'''\''t word2'\'''
   two=''\''word1 word2'\'''
   

   At this point echo $two would output 'word1 word2'

I'm looking for ways to remove the spare quotes that won't break the field splitting, won't break on more complex inputs like $three, and ideally don't rely on external commands. I also prefer not screwing with the IFS, but I don't think that's in the cards.

Reproduction script:

#!/usr/bin/env bash
set -x

# declare 2 vars and export them
function export_locals(){
    local one=1
    local two=$(echo word1 word2)
    local three=$(echo "word1 ain't word2")
    local # aka local -p
}

# insert vars into different local namespace
function import_locals(){
    echo ${one:-nah} ${two:-nope} # nothing up my sleeve
    local $(export_locals)
    local
    echo ${one:-nah} ${two:-nope} ${three:-nope}
}

function test_export_import_locals(){
    export_locals # just to show what it prints
    import_locals # bad attempt
    IFS=$'\n' import_locals # good (ish?) attempt
}

Answer 1

Note: I'm leaving the original answer below unchanged, but the underlying behavior changes in bash 5.1, where the output of local now behaves more like other setters.

---

I eventually iterated into a tolerable solution with external command xargs, which I've supplied below.

function import_locals(){
    local $(export_locals_xargs)
    local
}
function export_locals_xargs(){
    local one=1
    local two=$(echo word1 word2)
    local three=$(echo "word1 ain't word2")
    local | xargs printf "%s\n"
}
IFS=$'\n' import_locals

This will output:

one=1
three='word1 ain'\''t word2'
two='word1 word2'

Echoing the individual variables outputs:

one: 1
two: word1 word2
three: word1 ain't word2

---

bash 5.1+

function import_locals(){
    eval "$(export_locals_xargs)"
    local
}
function export_locals_xargs(){
    local one=1
    local two=$(echo word1 word2)
    local three=$(echo "word1 ain't word2")
    local -p
}
import_locals

This outputs:

declare -- one="1"
declare -- three="word1 ain't word2"
declare -- two="word1 word2"