http://docs.splunk.com/Documentation/Splunk/6.0.1/Installation/InstallonMacOS
Command line install directions are incomplete and incorrect.
hdid splunk_package_name.dmg
installer -pkg splunk.pkg -target /
Should be:
hdid splunk_package_name.dmg
cd /Volumes/SplunkForwarder 6.0.1/
installer -pkg .payload/Splunk Universal Forwarder.pkg -target /
Tested this on Mavericks 10.9.1
It might also be good to mention you need root or to execute all commands with sudo. But it notifies you of that fairly quickly.