#!/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"
IyEvYmluL2Jhc2gKcz0nc29tZXRoaW5nCkNBS0VfRlJPU1RJTkcoCiJpcyBzdXByZW1lIiwgCiJbaV1bYWdyZWVdIikgc29tZXRoaW5nIGVsc2UKc29tZXRoaW5nIG1vcmUKc29tZXRoaW5nIGVsc2UKQ0FLRV9GUk9TVElORygKImlzLiJraW5kYSIgbmVhdCIKImluIGZhY3QiLCAKIltpXVthZ3JlZV0iKSBzb21ldGhpbmcgZWxzZQpzb21ldGhpbmcgbW9yZScKcGVybCAtMDc3NyAtbmUgJ3doaWxlICgvQ0FLRV9GUk9TVElOR1woXHMqIihbXixdKikiL2cpIHskYT0kMTsgJGEgPX4gcy9eInwiJHwoXFIrKS8kMT8iICI6IiIvZ21lOyBwcmludCAiJGFcbiJ9JyA8PDwgIiRzIg==