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Execute a command at a given time

Terminal - Execute a command at a given time
echo "ls -l" | at midnight
2009-01-25 21:07:42
User: root
Functions: at echo
Execute a command at a given time

This is an alternative to cron which allows a one-off task to be scheduled for a certain time.


There are 3 alternatives - vote for the best!

Terminal - Alternatives
at midnight<<<'ls -l'

Know a better way?

If you can do better, submit your command here.

What others think

Good work - this is exactly what I've been looking for.

Comment by bazza 322 weeks and 2 days ago

Unfortunatly, nothing will be printed to the screen... you have to redirect the output to the current tty in order to see something :

echo "ls -l" >$(tty)| at midnight

it's only for the output of course

Comment by mrttlemonde 316 weeks and 2 days ago

Bravura! bravura! bravura!

Comment by Sonny 315 weeks and 6 days ago

mrttlemonde, your command is not exactly right with the quotes, i.e. it should be something like:

echo "ls -l >/dev/pts/3" |at 23:59

or we could also direct to a file:

echo "ls -lah >/foo/bar/ls.txt" |at 07:00
Comment by Buzzcp 310 weeks and 2 days ago

Thats Cool!!

Comment by gandulo 307 weeks ago

echo overload! :-)

Comment by mpb 301 weeks and 3 days ago

less-than less-than less-than "ls -l" at midnight

(where "less-than less-than less-than" is three less than symbols (these get "eaten" by commandlinefu text entry )

Comment by mpb 301 weeks and 3 days ago

Is there any way to make it work with, say... mplayer ? :)

Comment by sitaktif 299 weeks and 6 days ago

This is cool...

Comment by bakhru 276 weeks and 6 days ago

Be aware that the "at" command has a very important restriction. From the man page: "At and batch as presently implemented are not suitable when users are competing for resources." In other words, if your system is under a heavy load when the time comes to execute your "at" command, then your task might not run at all.

Some might see this as a feature, since it cuts down on time-release tasks when the system load is high, but in my case it caused an important set of overnight tests to mysteriously stop running. These days I use cron, which is less sensitive to system loads. I've also read good things about nqs (indeed, the "at" man page suggests it as an alternative), but haven't tried it.

Comment by willdye 269 weeks ago

I think I may have solved this problem.

And I'm wondering what really is the utility of "at" (or even cron). Sleep is enough. Why loop when we can just sleep up to the time to execute?

An "at" type script that runs once every 24hr - i.e. "sleep 86400; script.sh" - could parse a list of jobs and schedule, again using "at" style scripts, the ones on the list that matched the present year, day and month.

I must be missing something.

Comment by argv 239 weeks and 4 days ago

OK, time to spread the joy of crond!

You don't necessarily have to redirect stdout to a tty or logfile. In most crond implementations, the output of the commands in your crontab are mailed to your user by default.

Also @argv, the "at-type script" you are describing is basically the cron daemon. Where cron tables really excel over a simple script, though, is in their ability to describe specific and hard-to-express times, like running a task once every third day of the month at 4AM but only if it's Tuesday - which is a rather absurd example but hopefully I'm getting the point across.

If you ever wanted to do that for some reason, it's very simple:

echo '0 4 */3 2 /root/scripts/task.sh' | crontab

This will cause the system to execute the contents of "task.sh" with the sh shell (unless otherwise specified in the ENV or a shebang line) as your user, at whichever times and dates my ridiculous pattern applies to. :D

Anyway, cron tables are very powerful and once you get to know the ins and outs you'll realize there are few scheduling-related things you can't do with them. There's also special keywords and stuff, but think I've rambled enough for one day. :)

Comment by whisper 7 weeks and 4 days ago

Your point of view

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