1 //! This is an example of how to use `dup2` to replace the stdin and stdout
2 //! file descriptors.
3
4 #[cfg(not(windows))]
main()5 fn 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)]
main()53 fn main() {
54 unimplemented!()
55 }
56