Uh, it really depends on how you're storing your session data. If you have custom session handlers that store session data in the database, you can simply query the session data table and search for the "bob" variable in all the active sessions.
Typically, session data is all serialized into a single string before it's stored in a database, then unserialized as it's extracted. You might want to modify the way this happens if you really need to track common variables across multiple user sessions. Perhaps your session table can store active key/value pairs for sessions. This will require additional insert/select queries for each session write/read, but that's the price you pay!
You can perform a similar search throuh all the temp session files if you're NOT using custom sessions, though I can't imagine why you'd want to do that.
Take care,
Nik
http://www.bigaction.org/
SESSION tracking
