bash - Sleep until a specific time/date

Question

I want my bash script to sleep until a specific time. So, I want a command like "sleep" which takes no interval but an end time and sleeps until then.

The "at"-daemon is not a solution, as I need to block a running script until a certain date/time.

Is there such a command?

Answer 1

As mentioned by Outlaw Programmer, I think the solution is just to sleep for the correct number of seconds.

To do this in bash, do the following:

current_epoch=$(date +%s)
target_epoch=$(date -d '01/01/2010 12:00' +%s)

sleep_seconds=$(( $target_epoch - $current_epoch ))

sleep $sleep_seconds

To add precision down to nanoseconds (effectively more around milliseconds) use e.g. this syntax:

current_epoch=$(date +%s.%N)
target_epoch=$(date -d "20:25:00.12345" +%s.%N)

sleep_seconds=$(echo "$target_epoch - $current_epoch"|bc)

sleep $sleep_seconds

Note that macOS / OS X does not support precision below seconds, you would need to use coreutils from brew instead → see these instructions