Pipes

The std::Child struct represents a running child process, and exposes the
stdin, stdout and stderr handles for interaction with the underlying
process via pipes.

  1. use std::error::Error;
  2. use std::io::prelude::*;
  3. use std::process::{Command, Stdio};
  5. static PANGRAM: &'static str =
  6. "the quick brown fox jumped over the lazy dog\n";
  8. fn main() {
  9.     // Spawn the `wc` command
  10.     let process = match Command::new("wc")
  11.                                 .stdin(Stdio::piped())
  12.                                 .stdout(Stdio::piped())
  13.                                 .spawn() {
  14.         Err(why) => panic!("couldn't spawn wc: {}", why.description()),
  15.         Ok(process) => process,
  16.     };
  18.     // Write a string to the `stdin` of `wc`.
  19.     //
  20.     // `stdin` has type `Option<ChildStdin>`, but since we know this instance
  21.     // must have one, we can directly `unwrap` it.
  22.     match process.stdin.unwrap().write_all(PANGRAM.as_bytes()) {
  23.         Err(why) => panic!("couldn't write to wc stdin: {}",
  24.                            why.description()),
  25.         Ok(_) => println!("sent pangram to wc"),
  26.     }
  28.     // Because `stdin` does not live after the above calls, it is `drop`ed,
  29.     // and the pipe is closed.
  30.     //
  31.     // This is very important, otherwise `wc` wouldn't start processing the
  32.     // input we just sent.
  34.     // The `stdout` field also has type `Option<ChildStdout>` so must be unwrapped.
  35.     let mut s = String::new();
  36.     match process.stdout.unwrap().read_to_string(&mut s) {
  37.         Err(why) => panic!("couldn't read wc stdout: {}",
  38.                            why.description()),
  39.         Ok(_) => print!("wc responded with:\n{}", s),
  40.     }
  41. }