# 07 — Implement I/O redirection for commands

**Status:** open (post-core)
**Blocked by:** #03

## Syntax

```lua
`ls -l` > "output.txt"        -- redirect stdout to file
`ls -l` >> "output.txt"       -- append stdout to file
`cmd` 2> "err.txt"            -- redirect stderr to file
`cmd` 2>&1                    -- merge stderr into stdout
`cmd` < "input.txt"           -- redirect stdin from file
```

### Alternatively

```lua lush
`ls -l > output.txt`        -- redirect stdout to file
`ls -l >> output.txt`       -- append stdout to file
`cmd 2> err.txt`            -- redirect stderr to file
`cmd 2>&1`                    -- merge stderr into stdout
`cmd < input.txt`           -- redirect stdin from file
```

## Implementation

- Before `execvp()` in the child process, use `dup2()` to redirect file descriptors
- Parse redirection operators as part of the command syntax
- Open target files with appropriate flags:
  - `>` — `O_WRONLY | O_CREAT | O_TRUNC`
  - `>>` — `O_WRONLY | O_CREAT | O_APPEND`
  - `<` — `O_RDONLY`
- `2>&1` — `dup2(stdout_fd, STDERR_FILENO)`

## Challenge

`>` and `>>` conflict with Lua's greater-than and right-shift operators. Like piping, these operators must only be valid in command context. The parser can disambiguate because the left-hand side is a command expression.

## Alternatives

- Although shell redirection isn’t available, simple redirection can be achieved using the `io` library.

```lua lush
file = io.open("OUTFILE.txt", "w")
file:write(`ls /`.stdout)
file:close()
```