The at command allows the user to submit jobs or commands to the cron demon to be executed at a later time. A later time is generally anything from ten minutes up to the next few days. If you want to run a job later than a month stick in a crontab file.
When a job has been submitted, it will keep all its current environments including directory paths, unlike crontab, which doesn’t. All output from the jobs is mailed to the user, unless the output is redirected somewhere else, most probably a file.
Like cron, root can control who uses at, with the files at.allow and at.deny in /etc. But root is generally less strict on who can use at.
The basic format of at is:
at [-f script] [-m -l -r] [time] [date]
|-f script||is the ...|