The at command enables you to run a command once rather than at a repeating interval like cron does. This is useful if there is a processor-intensive task that you want to run after business hours so that other tasks aren't affected.
To schedule a one-time-only task use the at or batch command. To submit a job with the at command, you only need to enter the at command itself and the runtime you want, which is simply the date and time you want the job (process) to execute:
> at runtime
Pressing enter here, however, doesn't do anything but enter you into a new mode with a new prompt, most likely resembling the following:
What you will see varies among different distributions of Unix, but most times, this is exactly what will appear ...