Execute a command at a given time

echo "ls -l" | at midnight
This is an alternative to cron which allows a one-off task to be scheduled for a certain time.

247
By: root
2009-01-25 21:07:42

2 Alternatives + Submit Alt

What Others Think

Good work - this is exactly what I've been looking for.
bazza · 511 weeks and 3 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
mrttlemonde · 505 weeks and 3 days ago
Bravura! bravura! bravura!
Sonny · 505 weeks 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
Buzzcp · 499 weeks and 3 days ago
Thats Cool!!
gandulo · 496 weeks and 2 days ago
echo overload! :-)
mpb · 490 weeks and 4 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 )
mpb · 490 weeks and 4 days ago
Is there any way to make it work with, say... mplayer ? :)
sitaktif · 489 weeks and 1 day ago
This is cool...
bakhru · 466 weeks and 1 day 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.
willdye · 458 weeks and 1 day 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.
argv · 428 weeks and 6 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. :)
whisper · 196 weeks and 6 days ago
that is so good,,,,
xscorpion · 148 weeks and 5 days ago

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