TOPIC: How to use an external tool with a custom program?

I made a shell script to transform a mono sample to stereo and apply a convolution reverb on it. I call the script from anywhere and give the wav file as argument. This wav gets processed and replaced. I'm trying to use this script in Polyphone calling it with use an external tool and using as commandbut I only get a dialog "it wasn't possible to start the command". Any suggestions?

export the samples to anywhere, convert them there and import them in Polyphone (New Samples > Replace All)
regards bottrop

Thank you! But the problem is that the previous samples were mono and the new ones after processing are stereo. So, instead of asking to replace, it just adds them alongside. I even tried to rename the old ones adding an L at the end, but then I have to set up the other half of the samples again. Duplicating them and adding an R to the duplicated ones makes them all get replaced, but they get mono as if the duplications were just references and their relation get lost (L-R).
Regards, Luiz