#!/bin/bash
s='something
CAKE_FROSTING(
"is supreme", 
"[i][agree]") something else
something more
something else
CAKE_FROSTING(
"is."kinda" neat"
"in fact", 
"[i][agree]") something else
something more'
perl -0777 -ne 'while (/CAKE_FROSTING\(\s*"([^,]*)"/g) {$a=$1; $a =~ s/^"|"$|(\R+)/$1?" ":""/gme; print "$a\n"}' <<< "$s"