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November 2014


Sleep until a given date with subsecond resolution


sleepenh - an enhanced sleep program


sleepenh [[\,--warp|-w\/] \,INITIALTIME\/] \,TIMETOSLEEP\/


sleepenh is a program that can be used when there is a need to execute some functions periodically in a shell script. It was not designed to be accurate for a single sleep, but to be accurate in a sequence of consecutive sleeps.
After a successful execution, it returns to stdout the timestamp it finished running, that can be used as INITIALTIME to a successive execution of sleepenh.


-h, --help display this help and exit
-w, --warp warp resulting timestamp, when there is no need to sleep. An immediately following call of sleepenh with the resulting TIMESTAMP would most probably result in a real sleep.
-V, --version
output version information and exit


TIMETOSLEEP is a real number in seconds, with microseconds resolution (1 minute, 20 seconds and 123456 microseconds would be 80.123456).
INITIALTIME is a real number in seconds, with microseconds resolution. This number is system dependent. In GNU/Linux systems, it is the number of seconds since midnight 1970-01-01 GMT. Do not try to get a good value of INITIALTIME. Use the value supplied by a previous execution of sleepenh.
If you don’t specify INITIALTIME, it is assumed the current time.


An exit status greater or equal to 10 means failure. Known exit status:
0 Success.
1 Success. There was no need to sleep. (means that INITIALTIME + TIMETOSLEEP was greater than current time).
10 Failure. Missing command line arguments.
11 Failure. Did not receive SIGALRM.
12 Failure. Argument is not a number.
13 Failure. System error, could not get current time.


Suppose you need to send the char ’A’ to the serial port ttyS0 every 4 seconds. This will do that:

TIMESTAMP=$(sleepenh 0)
while true; do
# send the byte to ttyS0
echo -n "A" > /dev/ttyS0;

# just print a nice message on screen
echo -n "I sent ’A’ to ttyS0, time now is ";
sleepenh 0;
# wait the required time
TIMESTAMP=$(sleepenh $TIMESTAMP 4.0);


This program can be used to get the current time. Just execute:
sleepenh 0


It is not accurate for a single sleep. Short TIMETOSLEEPs will also not be accurate.



This manual page was written by Pedro Zorzenon Neto.
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