Linux at command with seconds precision

Question

I'm looking for a Linux command to launch another command at a specific time.

I know about the at command, but it gives me only minutes precision, and I need seconds precision. Is there an at option I'm not aware of? Or another command?

Answer 1

Use cron to run a script that calls the sleep command for the sub-miniute precision bit of it? So

sleep 10 ; foo.sh 

should run foo.sh 10 seconds after the command is called.

Answer 2

You can schedule your job at the nearest minute, then use alarm to get second-level precision. For an example in Python:

from signal import signal, setitimer, ITIMER_REAL, SIGALRM, alarm
from datetime import datetime, time
from sys import argv, exit
from time import sleep
at = datetime.combine(datetime.now(), time.fromisoformat(argv[1]))
class Done(Exception):
    pass
def _handler(signum, frame):
    print("The time is", datetime.now())
    raise Done()
setitimer(ITIMER_REAL, (at - datetime.now()).total_seconds())
signal(SIGALRM, _handler)
try:
    while True:
        sleep(1)
except Done:
    pass

Running:

$ python at-second.py 13:36:28
The time is 2022-07-06 13:36:28.000238

A limitation for this method:

only one alarm can be scheduled at any time

So if you need multiple events in a minute, you'd need to schedule the second one only after the first one is finished.