IOApp

App type that runs a cats.effect.IO. Shutdown occurs after the IO completes, as follows:

• If completed with ExitCode.Success, the main method exits and shutdown is handled by the platform.

• If completed with any other ExitCode, sys.exit is called with the specified code.

• If the IO raises an error, the stack trace is printed to standard error and sys.exit(1) is called.

When a shutdown is requested via a signal, the IO is canceled and we wait for the IO to release any resources. The process exits with the numeric value of the signal plus 128.

import cats.effect._
import cats.syntax.all._

object MyApp extends IOApp {
 def run(args: List[String]): IO[ExitCode] =
   args.headOption match {
     case Some(name) =>
       IO(println(s"Hello, ${name}.")).as(ExitCode.Success)
     case None =>
       IO(System.err.println("Usage: MyApp name")).as(ExitCode(2))
   }
}