#!/bin/sed -f
:paren
s/(\([^][(){}]*\))/\x01\1\x02/g;
t paren
s/{\([^][(){}]*\)}/\x03\1\x04/g;
t paren
s/\[\([^][(){}]*\)\]/\x05\1\x06/g;
t paren

s/\x01/)/g;
s/\x02/(/g;
s/\x03/}/g;
s/\x04/{/g;
s/\x05/]/g;
s/\x06/[/g;

s/$/\n/
:reverse
s/^\(.\)\(.*\n\)\(.*\)$/\2\1\3/
t reverse
s/\n//