# 25 — Environment variable expansion in commands

**Status:** done

## Problem

`$VAR` syntax works in Lua expressions but not inside commands:

```lua
print($PATH)        -- works: $PATH is lexed as TK_ENVVAR, expanded via getenv()
!echo $PATH         -- broken: $PATH is kept as literal text, passed unexpanded
```

The same applies to backtick commands:

```lua
local r = `echo $HOME`   -- $HOME is literal, not expanded
```

## Why it happens

The lexer has two separate paths for `$`:

1. **In Lua code** (`llex.c:667`): `$NAME` → `TK_ENVVAR` token → compiled to `getenv("NAME")` call
2. **In command mode** (`llex.c:518`): `$` without `{` is saved as a literal character in the command string buffer

Only `${expr}` interpolation works in commands — it enters a Lua expression context and returns the result inline. Bare `$NAME` is passed through verbatim.

Since commands are executed via `fork`/`exec` (not through `/bin/sh`), there is no shell to expand `$PATH` at runtime either.

## Expected behavior

`$VAR` should expand in commands the same way it does in Lua expressions:

```lua
!echo $HOME          -- should print /Users/nik
!echo $PATH          -- should print the PATH value
local r = `echo $HOME`  -- r.stdout should contain /Users/nik
```

## Workaround

Use `${expr}` interpolation:

```lua
!echo ${$HOME}
```

## Possible fix

In `read_command_body()` (`llex.c:518`), when `$` is followed by an identifier, emit the current command fragment and produce a `TK_ENVVAR`-equivalent expansion inline — similar to how `${expr}` already splits the command string to insert interpolated values.