Run a command once in three hours Post: 303027151

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Top Forums Shell Programming and Scripting Run a command once in three hours Post 303027151 by bakunin on Monday 10th of December 2018 08:05:32 AM

12-10-2018

Registered User

Quote:

Originally Posted by ginrkf

Hi it should run only every 9th time the script is running.If the file is there yes we need to execute hi and quit

This is an example of what is called "inter-process communication" because one process (the program to be started) needs some information of another process (the last instance of the program and when it ran lastly). There are only so many means for such inter-process communication:

- semaphores
- shared memory
- message queues

In this case we need a "semaphore". Not a "UNIX semaphore" (in UNIX there is a certain OS feature implementing semaphores), but something alike. We simply put a file somewhere with the "UNIX date", the numbers of seconds passed since Jan 1st 1970, of when the program ran the last time:

Code:

#! /bin/ksh

typeset last="/tmp/myfile"

if [ -f file ] ; then
     echo "hi"
else
     echo "Hello"
     UNIX Command---once in 3 hours
     echo $(date +'%s') > "$last"
fi

exit 0

Now we just need to read this file if it is there (otherwise we are running for the first time) and make the starting of the program conditional to that. Notice that 10800 = 3x3600, 3 hours in seconds and 4294967295 is 2^^32-1:

Code:

#! /bin/ksh

typeset    last="/tmp/myfile"
typeset -i now=$(date +'$s')

if [ -f file ] ; then
     echo "hi"
else
     echo "Hello"
     if ! [ -f "$last" ] ; then
          echo "4294967295" > "$last"
     fi
     if (( now - 10800 <= $(cat $last) )) ; then
          UNIX Command---once in 3 hours
          echo $(date +'%s') > "$last"
     fi
fi

exit 0

I hope this helps.

bakunin

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LEARN ABOUT DEBIAN

sleepenh

SLEEPENH(1)						      General Commands Manual						       SLEEPENH(1)

NAME

       sleepenh - an enhanced sleep program.

SYNOPSIS

       sleepenh [initial-time] sleep-time

DESCRIPTION

       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 exe-
       cution of sleepenh.

OPTIONS

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

ARGUMENTS

       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  exe-
       cution of sleepenh.
       If you don't specify initial-time, it is assumed the current-time.

EXIT STATUS

       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.

USAGE EXAMPLE

       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

HINT

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

       sleepenh 0

BUGS

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

SEE ALSO

       date(1), sleep(1).

AUTHOR

       This manual page was written by Pedro Zorzenon Neto.

								    2008/04/20							       SLEEPENH(1)