src/doc/rust-by-example/src/std_misc/process/pipe.md

   1 # Pipes
   2
   3 The `std::Child` struct represents a running child process, and exposes the
   4 `stdin`, `stdout` and `stderr` handles for interaction with the underlying
   5 process via pipes.
   6
   7 ```rust,ignore
   8 use std::error::Error;
   9 use std::io::prelude::*;
  10 use std::process::{Command, Stdio};
  11
  12 static PANGRAM: &'static str =
  13 "the quick brown fox jumped over the lazy dog\n";
  14
  15 fn main() {
  16     // Spawn the `wc` command
  17     let process = match Command::new("wc")
  18                                 .stdin(Stdio::piped())
  19                                 .stdout(Stdio::piped())
  20                                 .spawn() {
  21         Err(why) => panic!("couldn't spawn wc: {}", why.description()),
  22         Ok(process) => process,
  23     };
  24
  25     // Write a string to the `stdin` of `wc`.
  26     //
  27     // `stdin` has type `Option<ChildStdin>`, but since we know this instance
  28     // must have one, we can directly `unwrap` it.
  29     match process.stdin.unwrap().write_all(PANGRAM.as_bytes()) {
  30         Err(why) => panic!("couldn't write to wc stdin: {}",
  31                            why.description()),
  32         Ok(_) => println!("sent pangram to wc"),
  33     }
  34
  35     // Because `stdin` does not live after the above calls, it is `drop`ed,
  36     // and the pipe is closed.
  37     //
  38     // This is very important, otherwise `wc` wouldn't start processing the
  39     // input we just sent.
  40
  41     // The `stdout` field also has type `Option<ChildStdout>` so must be unwrapped.
  42     let mut s = String::new();
  43     match process.stdout.unwrap().read_to_string(&mut s) {
  44         Err(why) => panic!("couldn't read wc stdout: {}",
  45                            why.description()),
  46         Ok(_) => print!("wc responded with:\n{}", s),
  47     }
  48 }
  49 ```