Can Xamarin recognize warnings/errors produced by custom build commands?

I've created a bash script and am running it as a "Before Build" custom command. (I've also tried running it as a "Build" custom command). I've tried printing warnings to both STDOUT and STDERR, but Xamarin does not pick them up and display them in its "Errors" table.

Is it possible to have Xamarin pick up warnings/errors from custom build commands?