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Scala: Setting up shop: SBT on Linux

Installing SBT on Linux, and getting to know the basic commands.

Installing SBT (Scala Build Tool)

Installation details can be found in Scala SBT website https://www.scala-sbt.org/1.x/docs/Setup.html.

SBT First Steps

Once installed, you can start SBT by typing sbt in the terminal:

$ mkdir 01-hello-scala
$ cd 01-hello-scala
$ sbt
[warn] No sbt.version set in project/build.properties, base directory: /home/ubuntu/Development/git-repos/side-projects/grokking-scala/0-setting-up-shop/02-sbt-on-linux/01-hello-scala
[info] Set current project to root-01-hello-scala (in build file:/home/ubuntu/Development/git-repos/side-projects/grokking-scala/0-setting-up-shop/02-sbt-on-linux/01-hello-scala/)
[info] sbt server started at local:///home/ubuntu/.sbt/1.0/server/f63a8fbe3181e6c0f260/sock
sbt:root-01-hello-scala>
Note
The previous command will create a project/ directory

From the sbt prompt you can start the Scala REPL by typing console:

sbt:root-01-hello-scala> console
[info] Updating ...
[info] Done updating.
[info] Starting scala interpreter...
Welcome to Scala 2.12.6 (OpenJDK 64-Bit Server VM, Java 1.8.0_181).
Type in expressions for evaluation. Or try :help.
scala> 42
res1: Int = 42

scala> println("Hello to Jason Isaacs")
Hello to Jason Isaacs

scala> 1+2
res3: Int = 3
Problems starting the console?
The console task tries to compile the current project, and if an error is found the Scala REPL will not be started. In those case, you can use the task consoleQuick

Listing SBT available tasks

You can list the available sbt tasks by typing tasks at the sbt prompt.

Checking SBT version

You can check the sbt version by typing sbt sbtVersion in the terminal.

Scala REPL first steps

Scala provides a REPL (Read-Evaluate-Print-Loop) interpreter that can be used to write and run Scala programs in an interactive way. This tool includes some useful implicit imports to facilitate writing snippets. For example, you can use println without qualifying it because:

scala> println("Hello to Jason Isaacs")
Hello to Jason Isaacs

because the REPL automatically inserts the imports that map println to Console.println.

The Scala interpreter provides the following commands:

Command Description
:help Prints the help message and all the available commands
:cp Adds a JAR file to the classpath of the interpreter, so that you can refer to the classes inside the jar
E.g. :cp tools/junit.jar
:load Loads Scala file into the interpreter, so that all the definitions become available for the current snippet
:replay (:r) Resets the interpreter and replays all the previous commands
:quit (:q) Exits from the interpreter
:type Displays the type of an expression. The expression will not change the state of the interpreter
E.g. :type 1 + 2 // -> Int
:imports Displays the packages that are imported into the REPL

After you type an expression and type enter, the Scala interpreter will print the result prefixed by an automatically generated or user-defined name that identifies the computed value and that can be used subsequently.

scala> 1+2
res3: Int = 3

scala> res3 *2
res4: Int = 6
Packages in Scala
The type Int names the class Int in the package scala. Packages in Scala are similar to package in Java: they provide a mechanism for information hiding and structuring

Writing Scala Scripts

A Scala script is just a sequence of statements in a file that will be executed sequentially.

Projects

01 — Hello Scala

An empty project used to start the Scala interpreter from SBT.

02 — Hello Scala Script

Illustrates how to run Scala scripts saved in files using the Scala console :load <file>.