| SLEEP(1) | General Commands Manual | SLEEP(1) | 
sleep —
| sleep | seconds | 
sleep utility suspends execution for a minimum of
  seconds seconds, then exits. It is usually used to
  schedule the execution of other commands (see
  EXAMPLES below).
Note: The NetBSD
    sleep command will accept and honor a non-integer
    number of specified seconds. Note however, that if the request is for much
    more than 2.5 hours, any fractional seconds will be ignored. Permitting
    non-integral delays is a non-portable extension, and its use will decrease
    the probability that a shell script will execute properly on another
  system.
When the SIGINFO signal is received, an
    estimate of the number of seconds remaining to sleep is printed on the
    standard output.
sleep utility exits with one of the following
  values:
(sleep 1800; sh command_file
  >errors 2>&1)&This incantation would wait half an hour before running the script “command_file”. (See the at(1) utility.)
To repeatedly run a command (using csh(1)):
while (1) if (! -r zzz.rawdata) then sleep 300 else foreach i (*.rawdata) sleep 70 awk -f collapse_data $i >> results end break endif end
The scenario for a script such as this might be: a program currently running is taking longer than expected to process a series of files, and it would be nice to have another program start processing the files created by the first program as soon as it is finished (when zzz.rawdata is created). The script checks every five minutes for the file zzz.rawdata. When the file is found, processing the generated files (*.rawdata) is done courteously by sleeping for 70 seconds in between each awk job.
To wait until a particular time, the following, with some error checking added, might be used (using sh(1) on NetBSD):
END=$(( $( date -d "$1" +%s ) - START_TIME ))
while [ "${SECONDS}" -lt "${END}" ]
do
	sleep "$((END - SECONDS))"
done
where the argument ‘$1’ specifies the desired date
    and time in any format the -d option to the
    date(1) command accepts.
sleep command is expected to be
  IEEE Std 1003.2 (“POSIX.2”) compatible.
sleep utility appeared in
  Version 4 AT&T UNIX. Processing fractional
  seconds, and processing the seconds argument
  respecting the current locale, was added in NetBSD
  1.3. The ability to sleep for extended periods appeared in
  NetBSD 9.
sleep command cannot handle requests for durations
  much longer than about 250 billion years. Any such attempt will result in an
  error, and immediate termination. It is suggested that when there is a need
  for sleeps exceeding this period, the sleep command be
  executed in a loop, with each individual sleep
  invocation limited to 200 billion years approximately.
| January 26, 2019 | NetBSD 9.4 |