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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 (see
.Sx EXAMPLES
below).
.Pp
When the
.Dv SIGHUP
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
.Dq command_file .
(See the
.Xr at 1
utility.)
.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 $i >> results
end
break
endif
end
.Ed
.Pp
The scenario for a script such as this might be: a program currently
running is taking longer than expected to process a series of
files, and it would be nice to have
another program start processing the files created by the first
program as soon as it is finished (when zzz.rawdata is created).
The script checks every five minutes for the file zzz.rawdata.
When the file is found, processing the generated files (*.rawdata)
is done courteously by sleeping for 70 seconds in between each
awk job.
.Pp
To wait until a particular time, the following,
with some error checking added, might be used (using
.Xr sh 1
on
.Nx ) :
.Bd -literal -offset indent
END=$(( $( date -d "$1" +%s ) - START_TIME ))
while [ "${SECONDS}" -lt "${END}" ]
do
sleep "$((END - SECONDS))"
done
.Ed
.Pp
where the argument
.Sq \&$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 .
The ability to sleep for extended periods appeared in
.Nx 9 .
.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.
