Hi,

I am working on a small photography project. The goal is to take a snapshot with two cameras at the exact same instant. The camera shutters are triggered through a *nix command line application. So what I need to do is write a bash script that fires two instances of the app at the *exact* same time. Is there an easy way to do this through a bash script? Should I write a C prog instead? Any suggestions apreciated!

Thanks!

There is no way to do it at the *exact* same time
although you can come really close. A computer can
only execute one process at a time unless you have
multiple processors.

I wrote this really simple script to demonstrate
how to run the 2 programs concurrently
This will out put the same time/date

#!/bin/sh

date &
date

Putting the ampersand after a command runs it in background, the command interpreter goes on to process the next command.

On a fast PC the difference is going to be less than 1000th of a second (1 ms) between instance #1 and instance #2. If you're using a strobe, then you'll have to do something to turn off the thyristor so you get maximum burn time.

If I get what you want, consider --

tee

you can have output simultaneous output to more than one device. Like a port that triggers a shutter maybe

The /dev/null is capturing output that goers to the screen

The example above (from LogicG8) will have to be in a script file.

You could also try scheduling with "at".

Thanks for all of your suggestions. I'll experiment and post the results.

Still trying to figure out how get my keyspan usb->serial converter to bheave properly, but that is a story for another thread...