1 2set -e 3trap - USR1 4initial=$(trap) 5trap -- -l USR1 6added=$(trap) 7[ -n "$added" ] 8trap - USR1 9second=$(trap) 10[ "$initial" = "$second" ] 11eval "$added" 12added2=$(trap) 13added3=$(trap --) 14[ "$added" = "$added2" ] 15[ "$added2" = "$added3" ] 16trap -- - USR1 17third=$(trap) 18[ "$initial" = "$third" ] 19