wheres_my_mac.sh

/bin/echo '{"version": "1.1.0","host": "maps.google.com","request_address": true,"address_language": "en_US", "wifi_towers": [{"mac_address": "' $(/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -s | grep -o "\([0-9a-f]\{2\}:\)\{5\}[0-9a-f]\{2\}" | head -1 ) '","signal_strength": 8,"age": 0}]}'  | sed -e 's/" /"/' -e 's/ "/"/g' > /tmp/post.$$ && curl -X POST -d @/tmp/post.$$ http://www.google.com/loc/json | sed -e 's/{/\n/g' -e 's/,/\n/g'

From http://foss-boss.blogspot.com/2010/08/bash-oneliner-get-gps-location-street.html.