add command-line-io to hello-world

Author: bishabosha

_overviews/scala-book/command-line-io.md

@@ -9,7 +9,7 @@ num: 12
 outof: 54
 previous-page: two-notes-about-strings
 next-page: control-structures
-new-version: /scala3/book/introduction.html
+new-version: /scala3/book/taste-hello-world.html#ask-for-user-input
 ---
 
 

_overviews/scala3-book/taste-hello-world.md

@@ -7,9 +7,10 @@ previous-page: taste-intro
 next-page: taste-repl
 ---
 
+## Your First Scala Program
 
 A Scala 3 “Hello, world!” example goes as follows.
-First, put this code in a file named _Hello.scala_:
+First, put this code in a file named _hello.scala_:
 
 ```scala
 @main def hello() = println("Hello, world!")
@@ -22,17 +23,17 @@ It prints the `"Hello, world!"` string to standard output (STDOUT) using the `pr
 Next, compile the code with `scalac`:
 
 ```bash
-$ scalac Hello.scala
+$ scalac hello.scala
 ```
 
 If you’re coming to Scala from Java, `scalac` is just like `javac`, so that command creates several files:
 
 ```bash
 $ ls -1
-Hello$package$.class
-Hello$package.class
-Hello$package.tasty
-Hello.scala
+hello$package$.class
+hello$package.class
+hello$package.tasty
+hello.scala
 hello.class
 hello.tasty
 ```
@@ -50,6 +51,69 @@ Assuming that worked, congratulations, you just compiled and ran your first Scal
 
 > More information about sbt and other tools that make Scala development easier can be found in the [Scala Tools][scala_tools] chapter.
 
-[scala_tools]: {% link _overviews/scala3-book/scala-tools.md %}
+## Ask For User Input
+
+In our next example let's ask for the user's name before we greet them!
+
+There are several ways to read input from a command-line, but a simple way is to use the
+`readLine` method in the _scala.io.StdIn_ object. To use it, you need to first import it, like this:
+
+```scala
+import scala.io.StdIn.readLine
+```
+
+To demonstrate how this works, let’s create a little example. Put this source code in a file named _helloInteractive.scala_:
+
+```scala
+import scala.io.StdIn.readLine
+
+@main def helloInteractive() =
+  println("Please enter your name:")
+  val name = readLine()
+
+  println("Hello, " + name + "!")
+```
 
+In this code we save the result of `readLine` to a variable called `name`, we then
+use the `+` operator on strings to join `"Hello, "` with `name` and `"!"`, making one single string value. 
 
+> You can learn more about using `val` by reading [Variables and Data Types](/scala3/book/taste-vars-data-types.html).
+
+Then compile the code with `scalac`:
+
+```bash
+$ scalac helloInteractive.scala
+```
+Then run it with `scala helloInteractive`, this time the program will pause after asking for your name,
+and wait until you type a name and press return on the keyboard, looking like this:
+
+```bash
+$ scala helloInteractive
+Please enter your name:
+▌
+```
+
+When you enter your name at the prompt, the final interaction should look like this:
+
+```bash
+$ scala helloInteractive
+Please enter your name:
+Alvin Alexander
+Hello, Alvin Alexander!
+```
+
+### A Note about Imports
+
+As you saw in this application, sometimes certain methods, or other kinds of definitions that we'll see later,
+are not available unless you use an `import` clause like so:
+
+```scala
+import scala.io.StdIn.readLine
+```
+
+Imports help you write code in a few ways:
+  - you can put code in multiple files, to help avoid clutter, and to help navigate large projects.
+  - you can use a code library, perhaps written by someone else, that has useful functionality
+  - you can know where a certain definition comes from (especially if it was not written in the current file).
+
+[scala_tools]: {% link _overviews/scala3-book/scala-tools.md %}