SLEEP(1) | General Commands Manual | SLEEP(1) |
sleep
— suspend
execution for an interval of time
sleep |
seconds |
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.
The sleep
utility exits with one of the
following values:
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.
The sleep
command is expected to be
IEEE Std 1003.2 (“POSIX.2”)
compatible.
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 periods appeared in
NetBSD 9.0.
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.
January 26, 2019 | NetBSD 10.99 |