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.
use std::io::prelude::*;
use std::process::{Command, Stdio};
static PANGRAM: &'static str =
"the quick brown fox jumps over the lazy dog\n";
fn main() {
// Spawn the `wc` command
let mut cmd = if cfg!(target_family = "windows") {
let mut cmd = Command::new("powershell");
cmd.arg("-Command").arg("$input | Measure-Object -Line -Word -Character");
cmd
} else {
Command::new("wc")
};
let process = match cmd
.stdin(Stdio::piped())
.stdout(Stdio::piped())
.spawn() {
Err(why) => panic!("couldn't spawn wc: {}", why),
Ok(process) => process,
};
// Write a string to the `stdin` of `wc`.
//
// `stdin` has type `Option<ChildStdin>`, but since we know this instance
// must have one, we can directly `unwrap` it.
match process.stdin.unwrap().write_all(PANGRAM.as_bytes()) {
Err(why) => panic!("couldn't write to wc stdin: {}", why),
Ok(_) => println!("sent pangram to wc"),
}
// Because `stdin` does not live after the above calls, it is `drop`ed,
// and the pipe is closed.
//
// This is very important, otherwise `wc` wouldn't start processing the
// input we just sent.
// The `stdout` field also has type `Option<ChildStdout>` so must be unwrapped.
let mut s = String::new();
match process.stdout.unwrap().read_to_string(&mut s) {
Err(why) => panic!("couldn't read wc stdout: {}", why),
Ok(_) => print!("wc responded with:\n{}", s),
}
}