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# 1  
Old 10-07-2008
Date and time difference


I am starting a process at 9 pm today and want to exit the process by 5am, the next day. Every day at 9pm the shell script will be invoked by autosys.
But how can i monitor in my script for 5 am and stop the process ?

there may be a case where the script can start at 4.59 am and complete by even 6.00 am. So checking for (if current time >= 5 am ) will also wont work. Is there any function like date_diff or something else ?? How this can be acheived.

# 2  
Old 10-07-2008
You want the script to stop itself after 8 hours or 28800 seconds. Here is one somewhat clunky way -
#  script1.shl
   perl -e 'print time;'
stoptime=$(( start + 28800))
while [[ $now -lt stoptime ]]
      sleep 1
kill -USR1 $PPID

main script
trap "sleep 1; exit" USR1 
script1.shl &

#.............your code goes here..........

# 3  
Old 10-07-2008

The time calculating stuff i clear. What does the following does:

trap "sleep 1; exit" USR1 in the main code.

Please explain this in detail.

# 4  
Old 10-07-2008
When the child process gets past the time barrier it sends a SIGUSR1 to the parent. The trap in the parent grabs the signal (trap) sleeps long enough for the child to exit, then exits itself.

trap "command[s] to execute" signalname

to see all signals for your system try
kill -l

the -l is a lowercase L
# 5  
Old 10-07-2008
If you are using ksh93, you can use the alarm mechanism to simplify coding as shown in the following simple example

# abort after 10 seconds
alarm -r timedout +10

    print "Exceeded allowed time.  Aborting script ........"
    kill -9 $$

read dummy         # dummy wait - press ENTER to exit
exit 0


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