The essential Scala build tool tutorial

Create a basic empty SBT project

mkdir -p new-project
cd new-project
mkdir -p project
echo 'sbt.version=1.4.9' > project/build.properties

Compile the project

sbt compile

Recompile on code change

sbt '~compile'

~ watches for code changes. Press Enter to exit.

Create a source file

Run this command in another terminal window.

mkdir -p src/main/scala/
cat > src/main/scala/SimpleApp.scala << EOF
object SimpleApp extends App {
  println("It works")
}
EOF

Run continuously

Exit the ~compile command by pressing Enter

sbt '~run'

Change source to verify it works

sed -i -e 's/works/definitely works/' \
      src/main/scala/SimpleApp.scala

Add ScalaTest

echo 'libraryDependencies += "org.scalatest" %%' \
       '"scalatest" % "3.2.6" % Test' >> build.sbt

Create a test

mkdir -p src/test/scala/
cat > src/test/scala/SimpleTest.scala << EOF
import org.scalatest.funsuite._
final class SimpleTest extends AnyFunSuite {
  def sum(a: Int, b: Int): Int = ???
  test("sum works for 1 + 2 = 3") {
    assert(sum(1, 2) == 3)
  }
}
EOF

Test continuously

Exit previous ~run command by pressing Enter

sbt '~test'

Make it pass

sed -i -e 's/???/a + b/' src/test/scala/SimpleTest.scala

Use Scala 2.13

echo 'scalaVersion in ThisBuild := "2.13.5"' >> build.sbt

Add the sbt-native-packager plugin

echo 'addSbtPlugin("com.typesafe.sbt" % '\
       '"sbt-native-packager" % "1.8.1")' \
       > project/plugins.sbt

Enable sbt-native-packager

echo 'enablePlugins(JavaAppPackaging)' >> build.sbt

Package the app

sbt 'show dist'

Run packaged app

unzip -o -d /tmp/my-project \
        ./target/universal/new-project-0.1.0-SNAPSHOT.zip
/tmp/my-project/new-project-0.1.0-SNAPSHOT/bin/new-project

Dockerize your app

sbt docker:publishLocal

Run the docker image

docker run new-project:0.1.0-SNAPSHOT

Create a submodule

echo 'lazy val fizzbuzz = project' >> build.sbt

Compile the submodule

sbt fizzbuzz/compile

Add ScalaTest to submodule

echo '  .settings(libraryDependencies += "org.scalatest"' \
       '%% "scalatest" % "3.2.6" % Test)' >> build.sbt

Continually test the submodule

sbt '~fizzbuzz/test'

Create a method in the submodule

mkdir -p fizzbuzz/src/main/scala/
cat > fizzbuzz/src/main/scala/Fizz.scala << EOF
object Fizz {
  def buzz(n: Int): String = ???
}
EOF

Create a test in the submodule

mkdir -p fizzbuzz/src/test/scala/
cat > fizzbuzz/src/test/scala/FizzTest.scala << EOF
import org.scalatest.funsuite._
final class FizzTest extends AnyFunSuite {
  test("fizzBuzz for 4 is 4") {
    assert(Fizz.buzz(4) == "4")
  }
}
EOF

Pass the test

sed -i -e 's/???/s"$n"/' \
      fizzbuzz/src/main/scala/Fizz.scala

Make the app depend on the submodule

echo 'dependsOn(fizzbuzz)' >> build.sbt

Use the submodule in the app

sed -i -e 's/".*"/Fizz.buzz(args.last.toInt)/'\
      src/main/scala/SimpleApp.scala

Run the app with arguments

sbt "run --- 123"

Explicitly name the project

echo 'name := "new-project"' >> build.sbt

Explicitly version the project

echo 'version := "0.2"' >> build.sbt

Add JSoup Java library to main project

echo 'libraryDependencies += "org.jsoup" % "jsoup"' \
       '% "1.13.1"' >> build.sbt

Print all BBC News headlines

mkdir -p src/main/scala/
cat > src/main/scala/SimpleApp.scala << EOF
import org.jsoup.Jsoup
import scala.jdk.CollectionConverters._
object SimpleApp extends App {
  val doc = Jsoup.connect("http://www.bbc.com/news").get()
  val newsHeadlines = doc
    .select(".gs-c-promo-heading__title")
    .asScala
    .map(_.text().trim)
    .filter(_.nonEmpty)
  newsHeadlines.foreach(println)
}
EOF
sbt run

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