# Struct Child

1.0.0 · Source

    pub struct Child {
        pub stdin: Option<ChildStdin>,
        pub stdout: Option<ChildStdout>,
        pub stderr: Option<ChildStderr>,
        /* private fields */
    }

Expand description

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. You might find it helpful to do

ⓘ

    let stdin = child.stdin.take().expect("handle present");

to avoid partially moving the `child` and thus blocking yourself from calling functions on `child` while using `stdin`.

§`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().expect("handle present");

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().expect("handle present");

to avoid partially moving the `child` and thus blocking yourself from calling functions on `child` while using `stderr`.

## Implementations§

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### impl Child

1.0.0 · Source

#### pub fn kill(&mut self) -> Result<()>

Forces the child process to exit. If the child has already exited, `Ok(())` 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

    use std::process::Command;

    let mut command = Command::new("yes");
    if let Ok(mut child) = command.spawn() {
        child.kill().expect("command couldn't be killed");
    } else {
        println!("yes command didn't start");
    }

1.3.0 · Source

#### pub fn id(&self) -> u32

Returns the OS-assigned process identifier associated with this child.

##### §Examples

    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");
    }

1.0.0 · Source

#### 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

    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");
    }

1.18.0 · Source

#### 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

    use std::process::Command;

    let mut child = Command::new("ls").spawn()?;

    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}"),
    }

1.0.0 · Source

#### 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§

1.63.0 · Source§

### impl AsHandle for Child

Available on Windows only.
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#### fn as_handle(&self) -> BorrowedHandle<'_>

Borrows the handle. Read more
1.2.0 · Source§

### impl AsRawHandle for Child

Available on Windows only.
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#### fn as_raw_handle(&self) -> RawHandle

Extracts the raw handle. Read more
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### impl ChildExt for Child

Available on Unix only.
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#### fn send_signal(&self, signal: i32) -> Result<()>

🔬This is a nightly-only experimental API. (`unix_send_signal` #141975)
Sends a signal to a child process. Read more
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### impl ChildExt for Child

Available on Windows only.
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#### fn main_thread_handle(&self) -> BorrowedHandle<'_>

🔬This is a nightly-only experimental API. (`windows_process_extensions_main_thread_handle` #96723)
Extracts the main thread raw handle, without taking ownership
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### impl ChildExt for Child

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#### fn pidfd(&self) -> Result<&PidFd>

🔬This is a nightly-only experimental API. (`linux_pidfd` #82971)
Available on Linux only.
Obtains a reference to the `PidFd` created for this `Child`, if available. Read more
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#### fn into_pidfd(self) -> Result<PidFd, Self>

🔬This is a nightly-only experimental API. (`linux_pidfd` #82971)
Available on Linux only.
Returns the `PidFd` created for this `Child`, if available. Otherwise self is returned. Read more
1.16.0 · Source§

### impl Debug for Child

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
1.63.0 · Source§

### impl From<Child> for OwnedHandle

Available on Windows only.
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#### fn from(child: Child) -> OwnedHandle

Takes ownership of a `Child`’s process handle.

1.4.0 · Source§

### impl IntoRawHandle for Child

Available on Windows only.
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#### fn into_raw_handle(self) -> RawHandle

Consumes this object, returning the raw underlying handle. Read more

## Auto Trait Implementations§

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### impl Freeze for Child

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### impl RefUnwindSafe for Child

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### impl Send for Child

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### impl Sync for Child

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### impl Unpin for Child

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### impl UnwindSafe for Child

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.