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THE "AT" COMMAND


Today we have something simple that actually is a bit complicated to explain . . . . . it is about the command "at". This command "at" lets you execute a command or script at a later time, you can set the time in many different ways and even have the result mailed to you after the command has been executed.

Now, using "at" is not only just typing the command and hitting the enter-key  . . . there is a little more to it, so let me give an example. In the example we want to have the command "play /usr/share/sounds/KDE_Startup.wav" executed at 12:49 . . . . have a look what I see in the terminal:

QUOTE
$ at 12:49 -m
warning: commands will be executed using (in order) a) $SHELL b) login shell c) /bin/sh
at> play /usr/share/sounds/KDE_Startup.wav
at> <EOT>
job 7 at 2006-05-01 12:49

- On the 1st line you see the command "at 12:49 -m", meaning execute at 12:49 and the "-m" means mail me when the job is finished.
- On the 2nd line it will print some info about the at command and jump to line 3
- On the 3rd line you will see the "at>" prompt, at the "at>" prompt you type the command you want to have executed and you hit the enter-key again.
- On the 4th line you get the "at>" prompt appearing again, this time you press Ctrl+D and it will print <EOT>
- The 5th it will then automatically print the job number and the time the given command will be executed.



Next example: here we have a script "/usr/local/bin/backup-script" that we want executed at 12:32 . . . . Again, have a look what I see in the terminal:

QUOTE
# at 12:32 -m -f /usr/local/bin/backup-script
warning: commands will be executed using (in order) a) $SHELL b) login shell c) /bin/sh
job 8 at 2006-05-01 12:32

On the 1st line you see "at 12:32 -m" like in our first example  . . but after that comes "-f" meaning "from file" and "/usr/local/bin/backup-script" which is the path to the file/script I want to have executed.
On the 2nd and 3rd line you see the same as we saw on line 2 and 5 of our first example.


Okay . . hold on, we are almost there . . . . remember the job numbers? Well, they can come handy if you want to cancel the job before it runs.
First we use either "at -l" or "atq" to list the pending jobs:

QUOTE
$ at -l
7      2006-05-01 12:49 a bruno
8      2006-05-01 12:32 a root

And we see the number of the first job is "7"  . . . . now we remove that job with

CODE
$ atrm 7



Good . . . . now before I close off there is one last point I would like you to look at and that is the vast amount of different time formats you can use with the command "at" . . here is from the man-page:

QUOTE
       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 spe-
       cific time of day.  (If that time is already  past,  the  next  day  is
       assumed.)   You  may  also specify midnight, 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 MMDDYY or MM/DD/YY or DD.MM.YY.  The specifi-
       cation 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.

       For example, to run a job at 4pm three days from now, you would  do  at
       4pm  + 3 days
, to run a job at 10:00am on July 31, you would do at 10am
       Jul 31
and to run a job at 1am tomorrow, you would do at 1am  tomorrow.




Have Fun my friends, see you "at 8pm + 7 days" for a new Tip



Bruno


PS: See for another example and additional info: Linux.com



-- Jun 19 2006 --


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