1//! This is an example of how to use `dup2` to replace the stdin and stdout
2//! file descriptors.
3
4#[cfg(not(windows))]
5fn main() {
6    use rustix::io::{dup2, pipe};
7    use std::io::{BufRead, BufReader};
8    use std::mem::forget;
9
10    // Create some new file descriptors that we'll use to replace stdio's file
11    // descriptors with.
12    let (reader, writer) = pipe().unwrap();
13
14    // Acquire `OwnedFd` instances for stdin and stdout. These APIs are `unsafe`
15    // because in general, with low-level APIs like this, libraries can't assume
16    // that stdin and stdout will be open or safe to use. It's ok here, because
17    // we're directly inside `main`, so we know that stdin and stdout haven't
18    // been closed and aren't being used for other purposes.
19    let (mut stdin, mut stdout) = unsafe { (rustix::io::take_stdin(), rustix::io::take_stdout()) };
20
21    // Use `dup2` to copy our new file descriptors over the stdio file descriptors.
22    //
23    // These take their second argument as an `&mut OwnedFd` rather than the
24    // usual `impl AsFd` because they conceptually do a `close` on the original
25    // file descriptor, which one shouldn't be able to do with just a
26    // `BorrowedFd`.
27    dup2(&reader, &mut stdin).unwrap();
28    dup2(&writer, &mut stdout).unwrap();
29
30    // Then, forget the stdio `OwnedFd`s, because actually dropping them would
31    // close them. Here, we want stdin and stdout to remain open for the rest
32    // of the program.
33    forget(stdin);
34    forget(stdout);
35
36    // We can also drop the original file descriptors now, since `dup2` creates
37    // new file descriptors with independent lifetimes.
38    drop(reader);
39    drop(writer);
40
41    // Now we can print to "stdout" in the usual way, and it'll go to our pipe.
42    println!("hello, world!");
43
44    // And we can read from stdin, and it'll read from our pipe. It's a little
45    // silly that we connected our stdout to our own stdin, but it's just an
46    // example :-).
47    let mut s = String::new();
48    BufReader::new(std::io::stdin()).read_line(&mut s).unwrap();
49    assert_eq!(s, "hello, world!\n");
50}
51
52#[cfg(windows)]
53fn main() {
54    unimplemented!()
55}
56