SpringOne Platform 2019 Better Than BASH: Scripting Kotlin Speaker: Oliver Hughes, Staff Software Engineer, Pivotal Youtube: https://youtu.be/BHhp_1SGm64

1. Better than BASH -
Scripting & Automation with Kotlin
October 7–10, 2019
Austin Convention Center
Ollie Hughes - Staff Software Engineer - Pivotal
@olliehughes82

2. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
What 3 things do you find in every software
project?

3. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
• At least one caffeine addict
• At least one Magic the Gathering player
• At least one Bash / Powershell / DOS or Perl script over 50
lines long
3

4. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
What kind of things do we still write scripts for?

5. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
• Continuous Integration & Deployment (CI /CD)
• Publishing artefacts
• Interacting with CLI tools
• AdHoc manual or repetitive tasks.
• Generating a report for the boss from issue tracker
• Interacting with APIs
5

6. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Choosing the right tool

7. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
• Creating cloud / IaaS resources ➡ Terraform / Cloud Formation / …
• Creating archives from build artefacts ➡ Maven / Gradle / …
• Re-inventing the wheel - not using pre-built tools such as Concourse
Resources or well supported Jenkins plugins
Scripting Anti-Patterns
7

8. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
We can do better!
8
while getopts ":a:" FOUND "${@}";
do
case ${FOUND} in
a) app_name="${OPTARG}"
;;
:) printf "argument missing from -%s optionn"
$OPTARG
usage
exit 2
;;
?) printf "unknown option: -%sn" $OPTARG
usage
exit 2

9. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
• Modern
• Good tooling
• Productive
• Great ecosystem
Why use Kotlin for scripting
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10. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
• Standalone scripts for automation
• Supplementing CI pipelines & tools
• External configuration / YAML generation
• Embedded scripting within an application
• Dealing with API calls and serializing JSON
Good use cases for Kotlin Scripts
10

11. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Hello.kts
runner.sh
println(“Hello SpringOne”)
#!/bin/bash
kotlinc -script Hello.kts
A basic example
11

12. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
A basic example
12

13. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ 13
⚠ ⚠ 🐞 Bug alert 🐞 ⚠ ⚠

14. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
https://github.com/holgerbrandl/kscript
Install with sdkman
Install with brew (Mac only)
curl -s "https://get.sdkman.io" | bash
source ~/.bash_profile
sdk install kotlin
sdk install kscript
brew install holgerbrandl/tap/kscript
Simplifying the script execution with kscript
14

15. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Simplifying the script execution with kscript
15
Hello.kts
#!/usr/bin/env kscript
println(“Hello SpringOne”)

16. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Importing 3rd party libraries
16
#!/usr/bin/env kscript
@file:MavenRepository("jitpack", “https://jitpack.io"
SNAPSHOT”)
@file:DependsOn(“com.github.kotlin.kotlinx~cli:kotlinx-cli-
jvm:-SNAPSHOT”)
import kotlinx.cli.*

17. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Parsing arguments
17
#!/usr/bin/env kscript
for (arg in args) {
println("arg: ${arg}")
}

18. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
• Packaging a script
• Inline / eval a script
• Load script into IntelliJ IDEA or REPL
Other kscript features
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19. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Embedded scripting
19
Spring Cloud Contract Kotlin DSL uses a similar approach
KotlinScriptingHost().eval(File(“path/to/script.kts"))

20. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Testing Scripts
20
Then test framework has access to script like a normal import
@file:Import("path/to/externalScript.kts")

21. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Kscript vs Kotlin Scripting Support
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• Kscript still the better solution for standalone scripts
• Kotlin Scripting Support useful for more advanced use cases
• See https://github.com/Kotlin/KEEP/blob/master/proposals/scripting-
support.md

22. Unless otherwise indicated, these slides are © 2013-2019 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Kotlin Scripting Limitations
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• JVM startup penalty
• Distribution of JVM
• Kotlin/Native or GraalVM can solve these issues but dev cost is higher

23. Thanks
@ojhughes
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