When you submit an at job, it is assigned a job identification number along with the .a extension. This designation becomes the job's file name as well as its queue number.
Submitting an at job file involves the following steps:
Invoking the at utility and specifying a command execution time.
Typing a command or script to execute later.
For example, the following at job removes core files from the user account dsmith near midnight on the last day of July.
$ at 11:45pm July 31 at> rm /home/dsmith/*core* at> Press Control-d commands will be executed using /bin/csh job 933486300.a at Wed Jul 31 23:45:00 2019