finding unique ips in access log that have something in common

search for a string in access log, extract only ip address from matching line, sort the list of ip's and remove duplicates, output the [shortened] list...

for ip in `grep -i firefox /cygdrive/w/resin/log/access.log \
  | grep -o "^[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}" \
  | sort -u \
  | wc -l`; \
  do echo $ip; \
done