I know there are several ways in MacOS to open Safari with a given URL from the command line like

open -a Safari http://stackoverflow.comOr as an AppleScript

tell application "Safari" to open location "http://stackoverflow.com/"

in AppleScript, after opening Safari with URL

you may obtain the process object by

the proc object will have pid, bundle id and etc attached to it.

Also please note that Safari 5+ runs in a multi-process architecture: a master process and several rendering process, the above code will get you the master process only; rendering processes are not easily accessible, nor does it make much sense to control any individual rendering process.