在 2021 年的現代迷上寫指令工具（CLI: Command Line）聽起來有點不合常理？但身為開發者的浪漫就是想到可能就做一個試試！身為一個 Kotlin 開發者，如何用我們最愛的程式語言寫指令工具呢？在這場分享裡，我們將會綜覽幾個 CLI 框架及使用方式，並以實作一個 Generator 當範例，示範如何用 Kotlin 寫 CLI 並在各平台部署成原生程式。您也是老派風格的人嗎？歡迎一起來浪漫一下！

1. CLI
(Shengyou Fan)
COSCUP 2021
JVM
2021/08/01
Photo by Markus Spiske on Unsplash

2. JetBrains
Kotlin Open Source

3. Kotlin
—
• General-purpose
• Static typing
• OOP + FP
• Developed by
JetBrains
• Open Source
(Apache 2.0)
https://kotlinlang.org/

4. Command Line
2021

5. Shell (computing)
—
a shell is a computer program which exposes an operating
system's services to a human user or other program.
— From Wikipedia
GUI
CLI

6. !
Kotlin CLI

7. CLI
—
Input Output

8. IntelliJ IDEA
—

9. —

10. Kotlin
—
fun main() {
println("A sample CLI app")
}

11. Kotlin
—
fun main(args: Array<String>) {
args.forEachIndexed { index, string ->
println("($index): $string")
}
}

12. Fat Jar
—
plugins {
id("com.github.johnrengelman.shadow") version "6.1.0"
}
application {
mainClassName = "io.kraftsman.MainKt"
}

13. Jar
—
$ java -jar {cli_app_name}.jar

14. CLI
—
$ {cli_name} {command} arguments [options]
$ ./tree generate 10 --char=#

15. CLI
—
• / / Command
• / / Argument
• / / Option
•
•

16. "

17. Clikt
—
•
•
•
https://ajalt.github.io/clikt/

18. —
// gradle.properties
clikt_version=3.2.0
// build.gradle.kts
val clikt_version: String by project
dependencies {
implementation("com.github.ajalt.clikt:clikt:$ver")
}

19. —
class Hello: CliktCommand() {
override fun run() {
echo("Hello World!")
}
}
fun main(args: Array<String>) = Hello().main(args)

20. Command
—
class Database: CliktCommand() {
override fun run() = Unit
}
class Init: CliktCommand(help="Initialize the database") {
override fun run() {
echo("Initialized the database.")
}
}
class Drop: CliktCommand(help="Drop the database") {
override fun run() {
echo("Dropped the database.")
}
}
fun main(args: Array<String>) = Database()
.subcommands(Init(), Drop())
.main(args)

21. Argument
—
class Hello : CliktCommand() {
val name by argument()
override fun run() {
echo("Hello $name!")
}
}

22. Option
—
class Hello : CliktCommand() {
val count by option(help="Number of greetings")
.int()
.default(1)
val name by argument()
override fun run() {
for (i in 1..count) {
echo("Hello $name!")
}
}
}

23. #
ASCII

24. !

25. —
https://kotlinlang.org/docs/reference/native-overview.html https://www.graalvm.org/

26. GraalVM
—
•
•
https://www.graalvm.org

27. GraalVM
—
# SDKMAN
$ curl -s "https://get.sdkman.io" | bash
# GraalVM
$ sdk install java 21.1.0.r16-grl
# Java
$ sdk use java 21.1.0.r16-grl
# Native Image
$ gu install native-image

28. —
# Java
$ sdk use java 20.3.0.r11-grl
# Shadow FatJar
$ ./gradlew shadowJar
# Native Image
$ native-image -jar {jar_location}.jar
{cli_app_name}
--no-fallback
--report-unsupported-elements-at-runtime

29. —
• Shell
• CLI
• Clikt
• ASCII
•

30. Kotlin
—
Kotlin Tips
Line Telegram

31. https://tw.kotlin.tips
Tips
—
https://tw.intellij.tips

32. —
Coding
Kraftsman

33. (Shengyou Fan)
shengyou.fan@jetbrains.com
Q&A
—
CLI