==> Caveats
Data:    /usr/local/var/elasticsearch/elasticsearch_sgariepy/
Logs:    /usr/local/var/log/elasticsearch/elasticsearch_sgariepy.log
Plugins: /usr/local/var/lib/elasticsearch/plugins/
Config:  /usr/local/etc/elasticsearch/

To have launchd start elasticsearch at login:

ln -sfv /usr/local/opt/elasticsearch/*.plist ~/Library/LaunchAgents

Then to load elasticsearch now:

launchctl load ~/Library/LaunchAgents/homebrew.mxcl.elasticsearch.plist

Or, if you don't want/need launchctl, you can just run:

elasticsearch --config=/usr/local/opt/elasticsearch/config/elasticsearch.yml