# 05 — Implement environment variable access (read/write)

**Status:** done
**Blocked by:** #01

Add syntax for reading and writing environment variables directly from Lua.

## Option 1 — `export` keyword

```lua
local var = "my data"
export var                    -- exports existing local to env
export other_var = "my data"  -- creates + exports
```

- New reserved word `export` in lexer
- `export var` looks up the local's value by name and calls `setenv()`
- `export x = val` combines declaration with `setenv()`

## Option 2 — `$` sigil

```lua
local dir = $PWD              -- getenv("PWD")
$PWD = "/"                    -- setenv("PWD", "/")
$MY_ENV_VAR = "data"          -- setenv("MY_ENV_VAR", "data")
```

- `$NAME` as expression → `getenv("NAME")`, returns string or `nil`
- `$NAME = expr` as statement → `setenv("NAME", tostring(expr))`
- New token type in lexer for `$` + identifier

## Implementation touches

- `llex.c` / `llex.h` — new token(s) or reserved word
- `lparser.c` — new expression/statement rules
- Runtime calls `getenv()` / `setenv()` — standard C, no shell needed
- Non-existent env var → return `nil`