Migrating to OS X Mavericks breaks the ngrep utility. Doing:
sudo ngrep -d lo0 -q -W byline port 8080
stopped working where the process exits immediately. I didn't dig into the ngrep code, but was able to find a simple workaround by doing
sudo ngrep -q -W byline -d lo0 '' 'port 8080'
You can call that a lazy hack, but it work!