1. Search for '*.adoc' files
 2. Test if filename.adoc is newer than filename.html
 3. if so, run asciidoctor on it


 find . -name '*.adoc' | while read FILE; do [ ${FILE} -nt ${FILE%adoc}html ] && asciidoctor -q ${FILE} ; done

or put in a script:

 #! /bin/bash
 find . -name '*.adoc' | while read FILE; do
 if [ ${FILE} -nt ${FILE%adoc}html ]; then
 echo asciidoctor -q ${FILE}
 fi
 done

The one-line or the script can be run from crontab each minut:

 crontab -e

add a line

 * * * * * /home/joe/update_adoc.bash