Bro's input framework reads files asynchronously. See here
If using the input framework within a Bro script and running Bro against a small PCAP, often Bro will terminate before the input framework finishes reading in whatever file. suspend_input_continue is an example script that solves this problem.
Suspend packet processing until the input framework completes, then continue packet processing.
chmod +x blacklist_builder.sh
./blacklist_builder.sh > blacklist.file
bro -r small.pcap suspend_input_continue.bro