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.\"	@(#)sleep.1	8.3 (Berkeley) 4/18/94
.\"
.Dd January 26, 2019
.Dt SLEEP 1
.Os
.Sh NAME
.Nm sleep
.Nd suspend execution for an interval of time
.Sh SYNOPSIS
.Nm
.Ar seconds
.Sh DESCRIPTION
The
.Nm
utility suspends execution for a minimum of
.Ar seconds
seconds, then exits.
It is usually used to schedule the execution of other commands
.Po
see
.Sx EXAMPLES
below
.Pc .
.Pp
.Em Note :
The
.Nx
.Nm
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
.Em non-portable
extension, and its use will decrease the probability that a shell
script will execute properly on another system.
.Pp
When the
.Dv SIGINFO
signal is received, an estimate of the number of seconds remaining to
sleep is printed on the standard output.
.Sh EXIT STATUS
The
.Nm
utility exits with one of the following values:
.Bl -tag -width flag
.It Li \&0
On successful completion, or if the signal
.Dv SIGALRM
was received.
.It Li \&>0
An error occurred.
.El
.Sh EXAMPLES
To schedule the execution of a command for 1800 seconds later:
.Pp
.Dl (sleep 1800; sh command_file >errors 2>&1)&
.Pp
This incantation would wait half an hour before
running the script
.Ar command_file .
.Po
See the
.Xr at 1
utility
.Pc .
.Pp
To repeatedly run a command (using
.Xr csh 1 ) :
.Pp
.Bd -literal -offset indent -compact
while (1)
	if (! -r zzz.rawdata) then
		sleep 300
	else
		foreach i (*.rawdata)
			sleep 70
			awk -f collapse_data $i >> results
		end
		break
	endif
end
.Ed
.Pp
The scenario for a script such as this might be: a program currently
running is taking longer than expected to process a series of
files, and it would be nice to have
another program start processing the files created by the first
program as soon as it is finished
.Po
when
.Li zzz.rawdata
is created
.Pc .
The script checks every five minutes for the file
.Li zzz.rawdata .
When the file is found, processing the generated files
.Pq Li *.rawdata
is done courteously by sleeping for 70 seconds in between each
awk job.
.Pp
To wait until a particular time, the following,
with some error checking added, might be used
.Po
using
.Xr sh 1
on
.Nx
.Pc :
.Bd -literal -offset indent
END=$(( $( date -d "$1" +%s ) - START_TIME ))
while [ "${SECONDS}" -lt "${END}" ]
do
	sleep "$((END - SECONDS))"
done
.Ed
.Pp
where the argument
.Ql $1
specifies the desired date and time in any format the
.Fl d
option to the
.Xr date 1
command accepts.
.Sh SEE ALSO
.Xr at 1 ,
.Xr csh 1 ,
.Xr date 1 ,
.Xr sh 1 ,
.Xr nanosleep 2 ,
.Xr sleep 3
.Sh STANDARDS
The
.Nm
command is expected to be
.St -p1003.2
compatible.
.Sh HISTORY
A
.Nm
utility appeared in
.At v4 .
Processing fractional seconds, and processing the
.Ar seconds
argument respecting the current locale, was added in
.Nx 1.3 .
The ability to sleep for extended periods appeared in
.Nx 9.0 .
.Sh BUGS
This
.Nm
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
.Nm
command be executed in a loop, with each
individual
.Nm
invocation limited to 200 billion years
approximately.