open -a Safari http://stackoverflow.com
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.com
Or as an AppleScript
tell application "Safari" to open location "http://stackoverflow.com/"
in AppleScript, after opening Safari with URL
tell application "Safari" to open location "http://stackoverflow.com/"
you may obtain the process object by
tell application "System Events" to set proc to application process "Safari"
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.