Bdtjtk

I am trying to launch multiple instances of imagesnap simultaneously from a single bash script on a Mac. Also, it would be great to give (some of) the arguments by user input when running the script.

I have 4 webcams connected, and want to take series of images from each camera with a given interval. Being an absolute beginner with bash scripts, I don't know where to start searching. I have tested that 4 instances of imagesnap works nicely when running them manually from Terminal, but that's about it.

To summarise I'm looking to make a bash script that:

• run multiple instances of imagesnap.


• has user input for some of the arguments for imagesnap.


• ideally start all the imagesnap instances at (almost) the same time.

--EDIT--

After thinking about this I have a vague idea of how this script could be organised using the ability to take interval images with imagesnap -t x.xx:

• Run multiple scripts from within the main script

or

• Use subshells to run multiple instances of imagesnap




• Start each sub script or subshell in parallel if possible.




• Since each instance of imagesnap will run until terminated it would be great if they could all be stopped with a single command

the following quick hack (saved as run-periodically.sh) might do the right thing:

#!/bin/bash



interval=5

start=$(date +%s)



while true; do

    # run jobs in the background

    for i in 1 2 3 4; do

        "$@" &

    done

    # wait for all background jobs to finish

    wait

    # figure out how long we have to sleep

    end=$(date +%s)

    delta=$((start + interval - end))

    # if it's positive sleep for this amount of time

    if [ $delta -gt 0 ]; then

        sleep $delta || exit

    fi

    start=$((start + interval))

done

if you put this script somewhere appropriate and make it executable, you can run it like:

run-periodically.sh imagesnap arg1 arg2

but while testing, I ran with:

sh run-periodically.sh sh -c "date; sleep 2"

which will cause four copies of "start a shell that displays the date then waits a couple of seconds" to be run in parallel every interval seconds. if you want to run different things in the different jobs, then you might want to put them into this script explicitly or maybe another script which this one calls…

Some progress...

So far I have managed to start multiple versions of imagesnap. Here I create a new folder and subfolders for each webcam (webcam is the same in the code for testing).

Problem now is that I can't end all instances of imagesnap by terminating the script. Any ideas how to do this? Also, is wait useful/necessary at the end of the script?

#!/bin/bash



mkdir /Users/USER/Desktop/webcam/RUN1 #Modify later to take input: 1=RUN1, 2=RUN2, etc.



cd "$_" #Go to new directory



( #start first subshell

mkdir "FaceTime HD Camera1" #Make subfolder for webcam

cd "$_"

imagesnap -t 5 -d "FaceTime HD Camera" #save image every 5 sec

) & #End first subshell and run in parallel



(

mkdir "FaceTime HD Camera2"

cd "$_"

imagesnap -t 5 -d "FaceTime HD Camera"

) &



(

mkdir "FaceTime HD Camera3"

cd "$_"

imagesnap -t 5 -d "FaceTime HD Camera"

) &



(

mkdir "FaceTime HD Camera4"

cd "$_"

imagesnap -t 5 -d "FaceTime HD Camera"

) &