Linked by Dedoimedo on Wed 8th Dec 2010 17:40 UTC
Linux Here's the latest in our new series on OS tips from power users: a seemingly trivial task. You have a computer, most likely a laptop, that you wish to keep suspended while you're not working. For example, let's say overnight. At the same time, you wish to run a handful of maintenance tasks, like backups and cleanup, which you don't normally do during the day. So you need a mechanism that will send your machine to sleep, wake it up when necessary, run cron jobs, then send it back to sleep again.
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Script to "wake at" easily
by samueldr on Wed 8th Dec 2010 20:12 UTC
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I made a simple bash script to tell my computer to wake at a certain time without much fuss about the time format. It also corrects for a time which seems in the past but actually is in the future.

Here are some use case.
It's 13:00 (01:00 PM)
wake_at 15 #Will wake at 15:00
wake_at 16:45 #Will wake at 16:45
wake_at 8 #Will wake the next morning at 8

This means that when you go to sleep, you can go to a console (or anywhere you can type commands) and simply type the time you want your computer to wake at. Sure, you can't tell it to wake in a week with it, but it's not its intended use; it has a limited scope of 24 hours.

Here's the script:

wake_at=`date --date "$1" +%s`
now=`date +%s`

#Add a full day to the time if it is lesser than now...
#This allows calling `wake_at 8:00` the evening before.
if [ $wake_at -lt $now ]; then
let wake_at=$wake_at+86400

#Then execs rtcwake
exec rtcwake -l -t $wake_at -m no

Hope it helps!

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