# 06 — Implement piping between commands

**Status:** done

## Syntax

Pipes are written inside backtick strings using `|`:

```lua
local r = `ls -l | grep ".lua" | wc -l`
```

The `|` operator between backtick expressions remains Lua's bitwise OR — pipes only work *within* a single backtick command string.

## Implementation

Implemented in `lcmd.c` with two new functions:

- **`split_pipeline()`** — scans the command string for `|` outside single/double quotes, splits into an array of stage strings (up to 64 stages). Reuses the same quote-tracking logic as `parse_argv()`.

- **`exec_pipeline()`** — executes a multi-stage pipeline:
  1. `parse_argv()` each stage
  2. Creates N-1 inter-stage pipes + stdout/stderr capture pipes for the last stage
  3. Forks N children with appropriate stdin/stdout wiring
  4. Captures output from the last stage only
  5. Returns `{code=last_exit_code, stdout=captured, stderr=captured}`

`luaB_command()` calls `split_pipeline()` first. Single-stage commands (no `|`) fall through to the original single-command codepath unchanged.

## Behaviour

- Exit code is from the **last** pipeline stage (like bash)
- Only the last stage's stdout/stderr are captured in the result table
- Middle stages' stderr is inherited (goes to terminal)
- Quoted `|` characters (single or double quotes) are not pipe separators
- Empty pipeline stages (e.g. `cmd1 || cmd2` or leading/trailing `|`) are errors

## Tests

See `testes/lush/piping.lua`.