When you have questions such as this always consult the man pages. They can be very enlightening.
What it does
excerpt from at man page
at, batch, atq, atrm - queue, examine or delete jobs for later execution
at and batch read commands from standard input or a specified file
which are to be executed at a later time, using /bin/sh.
The usage of the tools:
Usage: at [-V] [-q x] [-f file] [-mldbv] timespec ...
at [-V] [-q x] [-f file] [-mldbv] -t time
at -c job ...
atq [-V] [-q x]
atrm [-V] job ...
at includes 4 commands (
batch). You use
batch to schedule the jobs,
atq to see what's scheduled, and
atrm to remove a job prior to it running.
$ at -f <cmd> timspec
The time to run the
at job can be specified in different ways.
excerpt form at man page
At allows fairly complex time specifications, extending the POSIX.2
standard. It accepts times of the form HH:MM to run a job at a
specific time of day. (If that time is already past, the next day is
assumed.) You may also specify mid‐ night, noon, or teatime (4pm) and
you can have a time-of-day suffixed with AM or PM for running in the
morning or the evening. You can also say what day the job will
be run, by giving a date in the form month-name day with an optional
year, or giving a date of the form MMDD[CC]YY, MM/DD/[CC]YY,
DD.MM.[CC]YY or [CC]YY-MM-DD. The specification of a date must
follow the specification of the time of day. You can also give times
like now + count time-units, where the time- units can be minutes,
hours, days, or weeks and you can tell at to run the job today by
suffixing the time with today and to run the job tomorrow by suffixing
the time with tomorrow.
Say you have this shell script.
$ cat mycrontest.sh
echo "It is now $(date +%T) on $(date +%A)"
It is now 18:37:42 on Friday
Sample at job submissions:
$ at -f mycrontest.sh 10pm tomorrow
job 14 at Sun Jul 8 22:00:00 2007
$ at -f mycrontest.sh 2:00 tuesday
job 15 at Tue Jul 10 02:00:00 2007
$ at -f mycrontest.sh 2:00 july 11
job 16 at Wed Jul 11 02:00:00 2007
$ at -f mycrontest.sh 2:00 next week
job 17 at Sat Jul 14 02:00:00 2007