Talking to terminals (and how they talk back) (KotlinConf 2026)

Have you ever wondered how Gradle renders multiple progress bars below the scrolling output? Or how a Linux installer renders full screen in the terminal? What about how curl somehow displays a progress bar despite having its output redirected to a file?

This talk will explore how command-line applications communicate with the terminal. From basic elements such as colors and the terminal size to advanced behavior like frame synchronization, images, and keyboard events.

Our journey will be in Kotlin, of course, and cover talking to OS-specific APIs, the challenges of JVM vs. Kotlin/Native, and finally some reusable libraries to make your life easier.

Modern terminals are powerful systems which can do a lot more than just display text. Let's use them to their full potential!

Video: coming soon!

Transcript

1. ./talking_to_te rmi nals ❯ And how they talk back! ❯
2. ./talking_to_te rmi nals whoa mi ❯ jakewharton ❯ And how they talk back! ❯
3. ❯ ./talking_to_te rmi nals And how they talk back! ❯ whoa mi jakewharton ❯
4. ❯ ./talking_to_te rmi nals And how they talk back! ❯ whoa mi jakewharton ❯ oldcomputr.com
5. ❯ ./talking_to_te rmi nals And how they talk back! ❯ whoa mi jakewharton ❯
6. (Live coding)
7. stdin stdout stderr
8. stdin stdout stderr app.kexe
9. stdin stdout stderr app.kexe Te rmi nal
10. stdin stdout stderr app.kexe Te rmi nal … 2> /dev/null
11. stdin stdout stderr app.kexe Te rmi nal … 2> /dev/null
12. stdin stdout stderr app.kexe Te rmi nal … 2> /dev/null … > stuff.txt
13. stdin stdout stderr app.kexe Te rmi nal … 2> /dev/null … > stuff.txt
14. stdin stdout stderr app.kexe Te rmi nal
15. (Live coding)
16. stdin stdout stderr curl Te rmi nal … > stuff.txt
17. stdin stdout stderr curl Te rmi nal … > stuff.txt ? ? ? ? ? ? ?
18. ? ? ? ? ? ? ? stdin stdout stderr curl … > stuff.txt /dev/tty
19. (Live coding)
20. oldcomputr.com ❯ ./talking_to_te rmi nals And how they talk back! ❯ whoa mi jakewharton ❯
21. oldcomputr.com ❯ ./talking_to_te rmi nals And how they talk back! ❯ whoa mi jakewharton ❯ logout
22. oldcomputr.com