Shell Programming and Scripting

Is there a way of saying I want to grab the time minus half an hour without converting time to a string?

I need to compare two system timestamps to see if there is half an hour between them for error messages going through our systems and I can't find any responses that don't use long conversions first. Is there such a thing? I have used the date command to get the two timestamps.

TIME=$(date '+%H:%M:%S')

What I want to say then is - if the first date is over half an hour older than the current date then remove a lock file we have put down, but I am unsure how to compare the two.

Any help would be greatly appreciated.

If we assume that the two systems are in the same region and that the clocks of these systems are at least set on the same day (hope so!!) and if we also assume that the seconds don't matter, you just need to do your calculations based on hours and minutes. I know that won't work around midnight, so just set a cron to run that anytime elese than around midnight.

I ignore how you'll get the time from both systems (ftp file, remsh, your logs names, etc), but I'd do the following arithmetic from both systems timestamps (ksh syntax):

(( minutes1=`date +"%H"`*60 + `date +"%M"` )) #system 1
(( minutes2=`date +"%H"`*60 + `date +"%M"` )) #system 2
(( minutesDiff=$minutes2-$minutes1 ))

if [ $minutesDiff > 30 ]
then
# do your stuff here
fi

Hope it'll point you to the right direction...

Also, if you use GNU date (from the shutils package), you can do something like this:

Code:

_past=$(date --date="30 minutes ago" +%Y%m%d%H%M)
_now=$(date +%Y%m%d%H%M)
_diff=$((_now-_past))
[[ $_diff -gt 30 ]] && echo "More that 30 minutes" || echo "Less than 30 minutes"

The advantages of date were high enough that it's been installed for use in some of our production scripts at work. Instead of replacing the date command, we have a seperate binary called gdate.

It's a great help for that reason alone.

Doh!
I realized what's wrong with mine...
If the hours are different, they won't match up...

If you don't feel like doing a bunch of evaluating and error handling, then the best way to do it would be above, when the poster grabs the minutes, and multiplies by 60...

Thanks for that. We now have a working monitoring script.