Working with the Command Line Compiler

This tutorial walks us through creating a Hello World application using the command line compiler.

Downloading the compiler

Every release ships with a standalone version of the compiler. We can download it from GitHub Releases. The latest release is 1.0.3.

Manual Install

Unzip the standalone compiler into a directory and optionally add the bin directory to the system path. The bin directory contains the scripts needed to compile and run Kotlin on Windows, OS X and Linux.

SDKMAN!

An easier way to install Kotlin on UNIX based systems such as OS X, Linux, Cygwin, FreeBSD and Solaris is by using SDKMAN!. Simply run the following in a terminal and follow any instructions:

   $ curl -s https://get.sdkman.io | bash

Next open a new terminal and install Kotlin with:

   $ sdk install kotlin

Homebrew

Alternatively, on OS X you can install the compiler via Homebrew.

   $ brew update
   $ brew install kotlin

Creating and running a first application

Create a simple application in Kotlin that displays Hello, World!. Using our favorite editor, we create a new file called hello.kt with the following:
```
fun main(args: Array<String>) {
    println("Hello, World!")
}
```
Compile the application using the Kotlin compiler
```
$ kotlinc hello.kt -include-runtime -d hello.jar
```
The -d option indicates what we want the output of the compiler to be called and may be either a directory name for class files or a .jar file name. The -include-runtime option makes the resulting .jar file self-contained and runnable by including the Kotlin runtime library in it. If you want to see all available options run
```
$ kotlinc -help
```
Run the application.
```
$ java -jar hello.jar
```

Compiling a library

If you’re developing a library to be used by other Kotlin applications, you can produce the .jar file without including the Kotlin runtime into it.

   $ kotlinc hello.kt -d hello.jar

Since binaries compiled this way depend on the Kotlin runtime you should make sure the latter is present in the classpath whenever your compiled library is used.

You can also use the kotlin script to run binaries produced by the Kotlin compiler:

   $ kotlin -classpath hello.jar HelloKt

HelloKt is the main class name that the Kotlin compiler generates for the file named hello.kt.

Running the REPL

We can run the compiler without parameters to have an interactive shell. We can type any valid Kotlin code and see the results.

Shell

Using the command line to run scripts

Kotlin can also be used as a scripting language. A script is a Kotlin source file (.kts) with top level executable code.

   import java.io.File

   val folders = File(args[0]).listFiles { file -> file.isDirectory() }
   folders?.forEach { folder -> println(folder) }

To run a script, we just pass the -script option to the compiler with the corresponding script file.

   $ kotlinc -script list_folders.kts <path_to_folder_to_inspect>