sleep(1) - NetBSD Manual Pages

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SLEEP(1)                NetBSD General Commands Manual                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 com-
     mands (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 sys-
     tem.

     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 run-
     ning 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 cre-
     ated).  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 IEEE Std 1003.2 (``POSIX.2'') compat-
     ible.


HISTORY

     A 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 peri-
     ods 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.

NetBSD 9.3                     January 26, 2019                     NetBSD 9.3