Module std::process

A module for working with processes.

This module is mostly concerned with spawning and interacting with child processes, but it also provides abort and exit for terminating the current process.

Spawning a process

The Command struct is used to configure and spawn processes:

use std::process::Command;

let output = Command::new("echo")
    .arg("Hello world")
    .output()
    .expect("Failed to execute command");

assert_eq!(b"Hello world\n", output.stdout.as_slice());

Several methods on Command, such as spawn or output, can be used to spawn a process. In particular, output spawns the child process and waits until the process terminates, while spawn will return a Child that represents the spawned child process.

Handling I/O

The stdout, stdin, and stderr of a child process can be configured by passing an Stdio to the corresponding method on Command. Once spawned, they can be accessed from the Child. For example, piping output from one command into another command can be done like so:

use std::process::{Command, Stdio};

// stdout must be configured with `Stdio::piped` in order to use
// `echo_child.stdout`
let echo_child = Command::new("echo")
    .arg("Oh no, a tpyo!")
    .stdout(Stdio::piped())
    .spawn()
    .expect("Failed to start echo process");

// Note that `echo_child` is moved here, but we won't be needing
// `echo_child` anymore
let echo_out = echo_child.stdout.expect("Failed to open echo stdout");

let mut sed_child = Command::new("sed")
    .arg("s/tpyo/typo/")
    .stdin(Stdio::from(echo_out))
    .stdout(Stdio::piped())
    .spawn()
    .expect("Failed to start sed process");

let output = sed_child.wait_with_output().expect("Failed to wait on sed");
assert_eq!(b"Oh no, a typo!\n", output.stdout.as_slice());

Note that ChildStderr and ChildStdout implement Read and ChildStdin implements Write:

use std::process::{Command, Stdio};
use std::io::Write;

let mut child = Command::new("/bin/cat")
    .stdin(Stdio::piped())
    .stdout(Stdio::piped())
    .spawn()
    .expect("failed to execute child");

// If the child process fills its stdout buffer, it may end up
// waiting until the parent reads the stdout, and not be able to
// read stdin in the meantime, causing a deadlock.
// Writing from another thread ensures that stdout is being read
// at the same time, avoiding the problem.
let mut stdin = child.stdin.take().expect("failed to get stdin");
std::thread::spawn(move || {
    stdin.write_all(b"test").expect("failed to write to stdin");
});

let output = child
    .wait_with_output()
    .expect("failed to wait on child");

assert_eq!(b"test", output.stdout.as_slice());

Structs

• Child
  Representation of a running or exited child process.
• ChildStderr
  A handle to a child process’s stderr.
• ChildStdin
  A handle to a child process’s standard input (stdin).
• ChildStdout
  A handle to a child process’s standard output (stdout).
• Command
  A process builder, providing fine-grained control over how a new process should be spawned.
• CommandArgs
  An iterator over the command arguments.
• CommandEnvs
  An iterator over the command environment variables.
• ExitCode
  This type represents the status code the current process can return to its parent under normal termination.
• ExitStatus
  Describes the result of a process after it has terminated.
• Output
  The output of a finished process.
• Stdio
  Describes what to do with a standard I/O stream for a child process when passed to the stdin, stdout, and stderr methods of Command.
• ExitStatusErrorExperimental
  Describes the result of a process after it has failed

Traits

• Termination
  A trait for implementing arbitrary return types in the main function.

Functions

• abort
  Terminates the process in an abnormal fashion.
• exit
  Terminates the current process with the specified exit code.
• id
  Returns the OS-assigned process identifier associated with this process.