# \[Elixir\] Tab Autocomplete Stage QP2 - How to detect TAB key?
**URL:** https://forum.codecrafters.io/t/elixir-tab-autocomplete-stage-qp2-how-to-detect-tab-key/15535
**Category:** Challenges
**Tags:** challenge:shell
**Created:** [November 15, 2025, 9:19pm UTC](https://forum.codecrafters.io/t/elixir-tab-autocomplete-stage-qp2-how-to-detect-tab-key/15535 "2025-11-15T21:19:23Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Illuminaxx](https://forum.codecrafters.io/u/Illuminaxx)
#### Post date: [November 15, 2025, 9:19pm UTC](https://forum.codecrafters.io/t/elixir-tab-autocomplete-stage-qp2-how-to-detect-tab-key/15535/1 "2025-11-15T21:19:23Z")
````auto
Hi everyone,
I'm working on the Shell challenge in Elixir and I'm stuck on Stage QP2 (Autocompletion - Builtin completion).
## Problem
When the test presses TAB, I receive spaces instead of the TAB character (byte 9):
- **Expected** : `"$ echo "`
- **Received** : `"$ ech "` (with spaces)
## What I've Tried
1. **ex_readline library** - Has a bug where tab completion only works with "/" prefix
2. **Custom implementation** with `IO.getn` - Detects TAB (byte 9) locally but not in test environment
3. **stty raw mode** - Works in TTY but CodeCrafters test environment is non-TTY
## My Implementation
```elixir
defp read_loop(buffer, completion_fn, prompt) do
input = IO.getn("", 1)
case input do
<<9>> when completion_fn != nil -> # TAB
new_buffer = handle_tab_completion(buffer, completion_fn, prompt)
read_loop(new_buffer, completion_fn, prompt)
# ... other cases
end
end
````
## Questions
1. Has anyone successfully completed this stage in Elixir?
2. Is there a specific library or approach recommended for Elixir?
3. How does the test environment simulate TAB key presses?
## Repository
All my attempts are documented here: [GitHub - Illuminaxx/codecrafters-shell-elixir](https://github.com/Illuminaxx/codecrafters-shell-elixir) See `AUTOCOMPLETE_NOTES.md` for detailed investigation
The Elixir ecosystem doesn’t have a mature readline library like Python’s `readline` or Rust’s `rustyline`, which makes this stage particularly challenging.
Any help would be greatly appreciated! 🙏
---
### Author:  [@andy1li](https://forum.codecrafters.io/u/andy1li)
#### Post date: [November 19, 2025, 3:45am UTC](https://forum.codecrafters.io/t/elixir-tab-autocomplete-stage-qp2-how-to-detect-tab-key/15535/4 "2025-11-19T03:45:33Z")
Hey @Illuminaxx, thanks for documenting everything so thoroughly!
Would you mind elaborating a bit on which specific issues you ran into when working with raw mode?
---
### Author:  [@andy1li](https://forum.codecrafters.io/u/andy1li)
#### Post date: [November 25, 2025, 12:15am UTC](https://forum.codecrafters.io/t/elixir-tab-autocomplete-stage-qp2-how-to-detect-tab-key/15535/6 "2025-11-25T00:15:27Z")
Closing this thread due to inactivity. If you still need assistance, feel free to reopen or start a new discussion!
---
### Author:  [@system](https://forum.codecrafters.io/u/system)
#### Post date: [November 30, 2025, 12:15am UTC](https://forum.codecrafters.io/t/elixir-tab-autocomplete-stage-qp2-how-to-detect-tab-key/15535/7 "2025-11-30T00:15:46Z")
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