# Issue #13 — Shell globbing

**Status:** done
**Blocked by:** #03, #04

## Problem

Commands inside backticks have no glob expansion. The argv parser treats `*`, `?`, and `{...}` as literal characters, so patterns like `ls *.lua` pass `*.lua` as a literal string to the command rather than expanding it to matching filenames.

```lua
-- currently: passes literal "*.lua" to ls
`ls *.lua`

-- expected: expands to matching files, like a shell would
`ls *.lua`  -- becomes ls foo.lua bar.lua ...
```

## Glob patterns to support

| Pattern | Description | Example |
|---------|-------------|---------|
| `*` | Match any characters (not `/`) | `*.lua` → `foo.lua bar.lua` |
| `?` | Match single character | `?.c` → `a.c b.c` |
| `**` | Recursive directory match | `**/*.lua` → `src/a.lua lib/b.lua` |
| `{a,b}` | Brace expansion | `*.{o,h}` → `foo.o bar.h` |
| `[abc]` | Character class | `[Mm]akefile` → `Makefile makefile` |

### Brace expansion details

Brace expansion happens *before* glob matching (same as bash). It's purely textual — not a filesystem operation:

```
echo {o,h}            → o h                (two words)
echo hello{o,h}       → helloo helloh      (prefix attached)
echo hello{world,go}  → helloworld hellogo (prefix attached)
echo *.{o,h}          → (expand braces first, then glob each: *.o *.h)
echo hello{world, x}  → hello{world, x}   (space inside braces = literal, no expansion)
```

Rules:
- Braces with commas and no spaces expand: `{a,b,c}` → `a b c`
- Prefix/suffix attach to each alternative: `pre{a,b}suf` → `preasuf prebsuf`
- Spaces inside braces cancel the expansion (treated literally)
- Nested braces: not needed initially

## Implementation

Glob expansion should happen in `lcmd.c` during argv construction, after tokenizing but before `execvp()`. Each token that contains glob metacharacters (`*`, `?`, `[`, `{`) gets expanded into zero or more filenames.

### Approach

1. **Brace expansion** (textual, first pass): scan each token for `{a,b,...}` patterns. Expand into multiple tokens. No filesystem access needed.

2. **Glob matching** (filesystem, second pass): for each token containing `*`, `?`, or `[`, call `glob(3)` (POSIX) to expand against the filesystem. If no matches, keep the literal token (like bash default).

3. **`**` recursive matching**: `glob(3)` doesn't support `**` on all platforms. May need a custom recursive walk, or use `GLOB_ALTDIRFUNC` where available. Could also use `nftw()` + `fnmatch()`.

### Where it runs

Expansion happens inside `parse_argv()` or in a post-processing step after `parse_argv()` returns. Each original token potentially becomes multiple argv entries.

### Quoting suppresses globbing

Quoted strings are already literal in `parse_argv()`:
- `"*.lua"` → literal `*.lua` (no expansion)
- `'*.o'` → literal `*.o` (no expansion)
- `\*` → literal `*` (backslash escape)

This matches shell behaviour — quoting suppresses glob expansion.

## Edge cases

- **No matches**: keep the literal pattern (bash default behaviour with `nullglob` off)
- **Dot files**: `*` should not match files starting with `.` unless the pattern starts with `.` (standard shell convention)
- **Expansion in pipelines**: each pipeline stage gets its own glob expansion
- **Very large expansions**: `**/*` in a large tree could produce thousands of entries — may need a reasonable limit

## Tests

```lua
-- basic wildcard
local r = `echo *.lua`
-- stdout should contain space-separated .lua files (non-empty)

-- no match keeps literal
local r = `echo *.nonexistent_extension_xyz`
assert(r.stdout == "*.nonexistent_extension_xyz\n")

-- quoted glob is literal
local r = `echo "*.lua"`
assert(r.stdout == "*.lua\n")

-- single-quoted glob is literal
local r = `echo '*.lua'`
assert(r.stdout == "*.lua\n")

-- brace expansion
local r = `echo {a,b,c}`
assert(r.stdout == "a b c\n")

-- brace expansion with prefix
local r = `echo hello{world,there}`
assert(r.stdout == "helloworld hellothere\n")

-- brace with spaces = no expansion
local r = `echo {a, b}`
assert(r.stdout == "{a, b}\n")

-- ? single char match
-- [abc] character class
```

## Files to modify

| File | Change |
|------|--------|
| `lcmd.c` | Add brace expansion + glob expansion in argv construction |