SLEEP(1)

NAME
sleep - suspend execution for an interval of time

SYNOPSIS
sleep seconds

DESCRIPTION
The 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.

EXIT STATUS
The sleep utility exits with one of the following values:

0   On successful completion, or if the signal SIGALRM was received.

>0  An error occurred.

EXAMPLES
To schedule the execution of a command for 1800 seconds later:

    (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.

SEE ALSO
at(1), csh(1), date(1), sh(1), nanosleep(2), sleep(3)

STANDARDS
The sleep command is expected to be p1003.2 compatible.

HISTORY
A sleep utility appeared in 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.

BUGS
This 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.