Shell Programming and Scripting

Hello everyone,

I am trying to write a script that will accomplish the following:

- query current system time and store result into a variable
- wait for some amount of time, say 300 seconds
- reset system time to earlier queried time + 1 second

I did some basic shell scripting (CSH mainly) and took an intro to perl class in 2000 but have not touched either since, and as a result I really have no idea how to accomplish this task. I'm also not really sure how to do the math on the time since the systemsetup -settime requires hh:mm:ss, so at 59 seconds I'll run into a problem

I'm currently using OS X 10.6.6 and /bin says I have access to bash, csh, ksh, tcsh, and zsh. I have no preference for which shell the script runs in, although echo $SHELL says my current default is bash, if that makes any difference.

I would also like to use argv (or something similar) to define how many cycles I'd like to process to repeat and possibly to define the wait time as well instead of hard coding these into the script.

Thanks in advance!

Xaiu

The right way to ajust the system time is to configure NTP
also see pool.ntp.org

Sounds like the OP wants to slow down the system clock, not keep it accurate. NTP would keep it accurate.

KevinGB is on the right track - the script isn't meant to adjust the system time to a reference time source to keep it accurate. I have an application that references the system time and I want to run that application for a set period of time, from say 12:00:00 to 12:05:00, tabulate the output, and then reset the system clock to 12:00:01 and run the application from 12:00:01 to 12:05:01 and compare the output to the previous run.

Actually, since I originally posted I realized that I don't need to query the current time at all. Instead I can just pass a clock time, wait period (in seconds), next cycle increment (in seconds), and an exit time into the script. This should get me around quite a number of the problems I was initially having and will hopefully simply the script down to something I can muddle my way through. Anyhow, I could do something like:

> script 12:00:00 300 1 12:00:05

which would hopefully:

- set the system time to 12:00:00
- wait for n seconds
- increment the input system time by increment (in this case 1 second)
- compare the result to the end time (passed in from script) and if new system time is less end time
- reset system time and loop to wait for n seconds

so in this scenario I should get 5 cycles that lasted for 5 minutes each and my timestamp on the data that is being collected would show:

1st cycle: 12:00:00 - 12:05:00

2nd cycle: 12:00:01 - 12:05:01

3rd cycle: 12:00:02 - 12:05:02

Thanks for your responses!

It is not advisible to change the system time in the manner proposed in post #1. Hard setting the date/time should only be done in single user mode armed with full knowledge of the effects on programs such as System Accounting and any Database Engines you may have.

What are you trying to do? We seem to have a proposed solution without knowing the problem.

If your system clock is a little bit fast, there should be a clock drift function (see "man date"). Or if you have access to a Time Server, use NTP as ctsgnb advises.

(Post drafted before seeing post #4). There has to be a better way which does not involve messing with the system clock.

Methyl, yes, great point.

This is a single user stand alone system running a custom simulation application for which I am collecting results at 1 second intervals. The application takes into account the time of day, which it gets from the system time. IE my data output from 12:00:00 - 12:59:59 will be different than the data output from 13:00:00 - 13:59:59, even though I have not changed any of the application parameters.

Since I can't change the behavior of the application (it getting it's simulation time from the system clock) I have been running the application for a set period of time and then re-adjusting the system clock by hand. I'm looking for a way to let the application run continuously, but appear as if it had been run for a set number of cycles with each cycle lasting a set period of time, and each cycle beginning from an incremental offset.

Hope that helps clarify the problem I'm trying to solve with the script.

Woudn't it be possible to play with the Timezone ?
Something like

Code:

TZ=$(($TZ+1)) && ./appli

or (FreeBSD)

Code:

$ export TZ=/usr/share/zoneinfo/Etc/UTC

Code:

$ date
Sun Feb 27 08:07:58 UTC 2011
$ export TZ=/usr/share/zoneinfo/Etc/GMT+1
$ date
Sun Feb 27 07:08:14 GMT+1 2011

---------- Post updated at 09:18 AM ---------- Previous update was at 09:11 AM ----------

[ctsgnb@shell ~/sand]$ export TZ=/usr/share/zoneinfo/Etc/UTC

Code:

$ date +'%H:%M:%S' && export TZ=/usr/share/zoneinfo/Etc/GMT+1 && date +'%H:%M:%S'
08:18:08
07:18:08
$