[main] initial parsing of command line args

build.sbt

@@ -6,6 +6,7 @@ scalaVersion := "2.12.8"
 
 libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.7" % "test"
 libraryDependencies += "org.typelevel" %% "cats-effect" % "1.3.0" withSources() withJavadoc()
+libraryDependencies += "com.github.scopt" %% "scopt" % "4.0.0-RC2"
 
 scalacOptions ++= Seq(
   "-feature",

src/main/scala/net/kemitix/s3thorp/Main.scala

@@ -5,13 +5,35 @@ import cats.effect.{ExitCode, IO, IOApp}
 
 object Main extends IOApp {
 
-  def parseArgs(args: List[String]): IO[Config] = IO.pure(Config("", ""))
+  def parseArgs(args: List[String]): IO[Config] = {
+    import scopt.OParser
+    val builder = OParser.builder[Config]
+    val configParser: OParser[Unit, Config] = {
+      import builder._
+      OParser.sequence(
+        programName("S3Thorp"),
+        head("s3thorp", "0.1.0"),
+        opt[String]('b', "bucket")
+          .action((str, c) => c.copy(bucket = str))
+          .text("S3 bucket name"),
+        opt[String]('p', "prefix")
+          .action((str, c) => c.copy(prefix = str))
+          .text("Prefix within the S3 Bucket")
+      )
+    }
+    val defaultConfig = Config("def-bucket", "def-prefix")
+    OParser.parse(configParser, args, defaultConfig) match {
+      case Some(config) => IO.pure(config)
+      case _ => IO.raiseError(new IllegalArgumentException)
+    }
+  }
 
   def putStrLn(value: String) = IO { println(value) }
 
   def sync(c: Config): IO[Unit] =
     for {
       _ <- putStrLn("S3Thorp - hashed sync for s3")
+      _ <- putStrLn(s"Bucket: ${c.bucket}, Prefix: ${c.prefix}")
     } yield ()
 
   def program(args: List[String]): IO[ExitCode] =