# Implementing TAB autocompletion in Elixir - Need guidance
**URL:** https://forum.codecrafters.io/t/implementing-tab-autocompletion-in-elixir-need-guidance/15685
**Category:** Challenges
**Tags:** challenge:shell
**Created:** [December 22, 2025, 6:25pm UTC](https://forum.codecrafters.io/t/implementing-tab-autocompletion-in-elixir-need-guidance/15685 "2025-12-22T18:25:13Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Illuminaxx](https://forum.codecrafters.io/u/Illuminaxx)
#### Post date: [December 22, 2025, 6:25pm UTC](https://forum.codecrafters.io/t/implementing-tab-autocompletion-in-elixir-need-guidance/15685/1 "2025-12-22T18:25:13Z")
Hi CodeCrafters team,
I’m working on the Shell challenge using Elixir and I’m stuck on Stage #QP2 (Tab Autocompletion - Builtin completion).
**The Problem:** The test expects TAB autocompletion to work, but Elixir/Erlang doesn’t have native readline support in standalone escripts like Node.js does with its built-in `readline` module.
**What I’ve Tried:**
- `:io.setopts(:standard_io, [expand_fun: &my_func/1])`
- `Application.put_env(:stdlib, :shell_expand_fun, &my_func/1)`
- Manual character-by-character reading with `IO.getn/2`
- Various terminal control sequences (ANSI, backspace, etc.)
None of these approaches work because Erlang’s `expand_fun` only works in an interactive Erlang shell, not in a compiled escript running standalone.
**The Issue:** In JavaScript (as shown in the community solutions), you can use Node.js’s `readline` module with a `completer` function:
javascript
```auto
readline.createInterface({
completer: (line) => { /* autocomplete logic */ }
});
```
Elixir doesn’t have an equivalent built-in feature. The only solution would be to use an external library like `erlang-readline` or implement a C NIF binding to libreadline.
**My Questions:**
1. Is it expected that Elixir users add external dependencies for this stage?
2. Can I modify `mix.exs` to add `{:erlang-readline, "~> 1.0"}` or similar?
3. Is there a CodeCrafters-specific solution I’m missing?
4. Should I skip this stage for now if no native solution exists?
**Current Test Output:**
```auto
Expected: "$ echo "
Received: "$ ech "
```
The autocompletion function is never triggered because there’s no way to hook into TAB handling in an Elixir escript without external libraries.
Any guidance would be greatly appreciated!
Thanks,
Illuminaxx
---
### Author:  [@andy1li](https://forum.codecrafters.io/u/andy1li)
#### Post date: [December 22, 2025, 6:25pm UTC](https://forum.codecrafters.io/t/implementing-tab-autocompletion-in-elixir-need-guidance/15685/2 "2025-12-22T18:25:14Z")
Hi, thanks for your post!
I’m currently out of the office for the holidays and will be back on January 5. I’ll get back to you as soon as possible once I return.
---
### Author:  [@andy1li](https://forum.codecrafters.io/u/andy1li)
#### Post date: [May 25, 2026, 8:23am UTC](https://forum.codecrafters.io/t/implementing-tab-autocompletion-in-elixir-need-guidance/15685/5 "2026-05-25T08:23:38Z")
Hey @Illuminaxx, sorry for the delayed response! Let me know if you’d still like assistance with this.
---
### Author:  [@system](https://forum.codecrafters.io/u/system)
#### Post date: [May 31, 2026, 6:13pm UTC](https://forum.codecrafters.io/t/implementing-tab-autocompletion-in-elixir-need-guidance/15685/7 "2026-05-31T18:13:37Z")
This topic was automatically closed 5 days after the last reply. New replies are no longer allowed.