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 V7

at

AT(1)							      General Commands Manual							     AT(1)

NAME

       at - execute commands at a later time

SYNOPSIS

       at time [ day ] [ file ]

DESCRIPTION

       At  squirrels  away a copy of the named file (standard input default) to be used as input to sh(1) at a specified later time.  A cd(1) com-
       mand to the current directory is inserted at the beginning, followed by assignments to all environment variables.  When the script is  run,
       it uses the user and group ID of the creator of the copy file.

       The  time  is  1  to 4 digits, with an optional following `A', `P', `N' or `M' for AM, PM, noon or midnight.  One and two digit numbers are
       taken to be hours, three and four digits to be hours and minutes.  If no letters follow the digits, a 24 hour clock time is understood.

       The optional day is either (1) a month name followed by a day number, or (2) a day of the week; if the word `week'  follows  invocation	is
       moved seven days further off.  Names of months and days may be recognizably truncated.  Examples of legitimate commands are

	      at 8am jan 24
	      at 1530 fr week

       At  programs  are  executed by periodic execution of the command /usr/lib/atrun from cron(8).  The granularity of at depends upon how often
       atrun is executed.

       Standard output or error output is lost unless redirected.

FILES

       /usr/spool/at/yy.ddd.hhhh.uu
       activity to be performed at hour hhhh of year day ddd of year yy.  uu is a unique number.
       /usr/spool/at/lasttimedone contains hhhh for last hour of activity.
       /usr/spool/at/past directory of activities now in progress
       /usr/lib/atrun program that executes activities that are due
       pwd(1)

SEE ALSO

       calendar(1), cron(8)

DIAGNOSTICS

       Complains about various syntax errors and times out of range.

BUGS

       Due to the granularity of the execution of /usr/lib/atrun, there may be bugs in scheduling things almost exactly 24 hours into the future.

																	     AT(1)