Struct std::process::Child
pub struct Child { pub stdin: Option<ChildStdin>, pub stdout: Option<ChildStdout>, pub stderr: Option<ChildStderr>, // some fields omitted }
Representation of a running or exited child process.
This structure is used to represent and manage child processes. A child process is created via the Command
struct, which configures the spawning process and can itself be constructed using a builder-style interface.
There is no implementation of Drop
for child processes, so if you do not ensure the Child
has exited then it will continue to run, even after the Child
handle to the child process has gone out of scope.
Calling wait
(or other functions that wrap around it) will make the parent process wait until the child has actually exited before continuing.
Warning
On some systems, calling wait
or similar is necessary for the OS to release resources. A process that terminated but has not been waited on is still around as a “zombie”. Leaving too many zombies around may exhaust global resources (for example process IDs).
The standard library does not automatically wait on child processes (not even if the Child
is dropped), it is up to the application developer to do so. As a consequence, dropping Child
handles without waiting on them first is not recommended in long-running applications.
Examples
use std::process::Command; let mut child = Command::new("/bin/cat") .arg("file.txt") .spawn() .expect("failed to execute child"); let ecode = child.wait() .expect("failed to wait on child"); assert!(ecode.success());
Fields
stdin: Option<ChildStdin>
The handle for writing to the child’s standard input (stdin), if it has been captured. To avoid partially moving the child
and thus blocking yourself from calling functions on child
while using stdin
, you might find it helpful:
let stdin = child.stdin.take().unwrap();
stdout: Option<ChildStdout>
The handle for reading from the child’s standard output (stdout), if it has been captured. You might find it helpful to do
let stdout = child.stdout.take().unwrap();
to avoid partially moving the child
and thus blocking yourself from calling functions on child
while using stdout
.
stderr: Option<ChildStderr>
The handle for reading from the child’s standard error (stderr), if it has been captured. You might find it helpful to do
let stderr = child.stderr.take().unwrap();
to avoid partially moving the child
and thus blocking yourself from calling functions on child
while using stderr
.
Implementations
impl Child
pub fn kill(&mut self) -> Result<()>
Forces the child process to exit. If the child has already exited, an InvalidInput
error is returned.
The mapping to ErrorKind
s is not part of the compatibility contract of the function.
This is equivalent to sending a SIGKILL on Unix platforms.
Examples
Basic usage:
use std::process::Command; let mut command = Command::new("yes"); if let Ok(mut child) = command.spawn() { child.kill().expect("command wasn't running"); } else { println!("yes command didn't start"); }
pub fn id(&self) -> u32
Returns the OS-assigned process identifier associated with this child.
Examples
Basic usage:
use std::process::Command; let mut command = Command::new("ls"); if let Ok(child) = command.spawn() { println!("Child's ID is {}", child.id()); } else { println!("ls command didn't start"); }
pub fn wait(&mut self) -> Result<ExitStatus>
Waits for the child to exit completely, returning the status that it exited with. This function will continue to have the same return value after it has been called at least once.
The stdin handle to the child process, if any, will be closed before waiting. This helps avoid deadlock: it ensures that the child does not block waiting for input from the parent, while the parent waits for the child to exit.
Examples
Basic usage:
use std::process::Command; let mut command = Command::new("ls"); if let Ok(mut child) = command.spawn() { child.wait().expect("command wasn't running"); println!("Child has finished its execution!"); } else { println!("ls command didn't start"); }
pub fn try_wait(&mut self) -> Result<Option<ExitStatus>>
Attempts to collect the exit status of the child if it has already exited.
This function will not block the calling thread and will only check to see if the child process has exited or not. If the child has exited then on Unix the process ID is reaped. This function is guaranteed to repeatedly return a successful exit status so long as the child has already exited.
If the child has exited, then Ok(Some(status))
is returned. If the exit status is not available at this time then Ok(None)
is returned. If an error occurs, then that error is returned.
Note that unlike wait
, this function will not attempt to drop stdin.
Examples
Basic usage:
use std::process::Command; let mut child = Command::new("ls").spawn().unwrap(); match child.try_wait() { Ok(Some(status)) => println!("exited with: {}", status), Ok(None) => { println!("status not ready yet, let's really wait"); let res = child.wait(); println!("result: {:?}", res); } Err(e) => println!("error attempting to wait: {}", e), }
pub fn wait_with_output(self) -> Result<Output>
Simultaneously waits for the child to exit and collect all remaining output on the stdout/stderr handles, returning an Output
instance.
The stdin handle to the child process, if any, will be closed before waiting. This helps avoid deadlock: it ensures that the child does not block waiting for input from the parent, while the parent waits for the child to exit.
By default, stdin, stdout and stderr are inherited from the parent. In order to capture the output into this Result<Output>
it is necessary to create new pipes between parent and child. Use stdout(Stdio::piped())
or stderr(Stdio::piped())
, respectively.
Examples
use std::process::{Command, Stdio}; let child = Command::new("/bin/cat") .arg("file.txt") .stdout(Stdio::piped()) .spawn() .expect("failed to execute child"); let output = child .wait_with_output() .expect("failed to wait on child"); assert!(output.status.success());
Trait Implementations
fn as_raw_handle(&self) -> RawHandle
Extracts the raw handle, without taking any ownership.
impl ChildExt for Child
fn pidfd(&self) -> Result<&PidFd>
fn take_pidfd(&mut self) -> Result<PidFd>
impl Debug for Child
fn fmt(&self, f: &mut Formatter<'_>) -> Result
Formats the value using the given formatter. Read more
fn from(child: Child) -> OwnedHandle
Performs the conversion.
Auto Trait Implementations
impl RefUnwindSafe for Child
impl Send for Child
impl Sync for Child
impl Unpin for Child
impl UnwindSafe for Child
Blanket Implementations
impl<T> From<T> for T
pub fn from(t: T) -> T
Performs the conversion.
pub fn into(self) -> U
Performs the conversion.
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
Performs the conversion.
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/process/struct.Child.html