sleepenh (1)

sleepenh [initial-time] sleep-time

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 initial-time to a successive execution of sleepenh.

There are no command line options. Run it without any option to get a brief help and version.

sleep-time is a real number in seconds, with microseconds resolution (1 minute, 20 seconds and 123456 microseconds would be 80.123456).

initial-time 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 initial-time. Use the value supplied by a previous execution of sleepenh.

If you don't specify initial-time, 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 initial-time + sleep-time 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:

#!/bin/sh 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`;

done

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

sleepenh 0

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

date(1), sleep(1).

This manual page was written by Pedro Zorzenon Neto.