.z.ts:f

Where f is a unary function, .z.ts is evaluated on intervals of the timer variable set by system command \t.

q)/ set the timer to 1000 milliseconds
q)\t 1000
q)/ argument x is the timestamp scheduled for the callback
q)/ .z.ts is called once per second and returns the timestamp
q).z.ts:{0N!x}
q)2010.12.16D17:12:12.849442000
2010.12.16D17:12:13.849442000
2010.12.16D17:12:14.849442000
2010.12.16D17:12:15.849442000
2010.12.16D17:12:16.849442000

When kdb+ has completed executing a script passed as a command-line argument, and if there are no open sockets nor a console, kdb+ will exit. The timer alone is not enough to stop the process exiting – it must have an event source which is a file descriptor (socket, console, or some plugin registering a file descriptor and callback via the C API sd1 function).