process.rs.html -- source
Description: Source to the Rust file `src/libstd/process.rs`.
Keywords: rust, rustlang, rust-lang

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    //! 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:
    //!
    //! ```no_run
    //! 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:
    //!
    //! ```no_run
    //! 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`]:
    //!
    //! ```no_run
    //! 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");
    //!
    //! {
    //!     // limited borrow of stdin
    //!     let stdin = child.stdin.as_mut().expect("failed to get stdin");
    //!     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());
    //! ```
    //!
    //! [`abort`]: fn.abort.html
    //! [`exit`]: fn.exit.html
    //!
    //! [`Command`]: struct.Command.html
    //! [`spawn`]: struct.Command.html#method.spawn
    //! [`output`]: struct.Command.html#method.output
    //!
    //! [`Child`]: struct.Child.html
    //! [`ChildStdin`]: struct.ChildStdin.html
    //! [`ChildStdout`]: struct.ChildStdout.html
    //! [`ChildStderr`]: struct.ChildStderr.html
    //! [`Stdio`]: struct.Stdio.html
    //!
    //! [`stdout`]: struct.Command.html#method.stdout
    //! [`stdin`]: struct.Command.html#method.stdin
    //! [`stderr`]: struct.Command.html#method.stderr
    //!
    //! [`Write`]: ../io/trait.Write.html
    //! [`Read`]: ../io/trait.Read.html

    #![stable(feature = "process", since = "1.0.0")]

    use crate::io::prelude::*;

    use crate::ffi::OsStr;
    use crate::fmt;
    use crate::fs;
    use crate::io::{self, Initializer, IoSlice, IoSliceMut};
    use crate::path::Path;
    use crate::str;
    use crate::sys::pipe::{read2, AnonPipe};
    use crate::sys::process as imp;
    use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};

    /// 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`](#method.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 system, 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
    ///
    /// ```should_panic
    /// 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());
    /// ```
    ///
    /// [`Command`]: struct.Command.html
    /// [`Drop`]: ../../core/ops/trait.Drop.html
    /// [`wait`]: #method.wait
    #[stable(feature = "process", since = "1.0.0")]
    pub struct Child {
        handle: imp::Process,

        /// The handle for writing to the child's standard input (stdin), if it has
        /// been captured.
        #[stable(feature = "process", since = "1.0.0")]
        pub stdin: Option<ChildStdin>,

        /// The handle for reading from the child's standard output (stdout), if it
        /// has been captured.
        #[stable(feature = "process", since = "1.0.0")]
        pub stdout: Option<ChildStdout>,

        /// The handle for reading from the child's standard error (stderr), if it
        /// has been captured.
        #[stable(feature = "process", since = "1.0.0")]
        pub stderr: Option<ChildStderr>,
    }

    impl AsInner<imp::Process> for Child {
        fn as_inner(&self) -> &imp::Process {
            &self.handle
        }
    }

    impl FromInner<(imp::Process, imp::StdioPipes)> for Child {
        fn from_inner((handle, io): (imp::Process, imp::StdioPipes)) -> Child {
            Child {
                handle,
                stdin: io.stdin.map(ChildStdin::from_inner),
                stdout: io.stdout.map(ChildStdout::from_inner),
                stderr: io.stderr.map(ChildStderr::from_inner),
            }
        }
    }

    impl IntoInner<imp::Process> for Child {
        fn into_inner(self) -> imp::Process {
            self.handle
        }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for Child {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("Child")
                .field("stdin", &self.stdin)
                .field("stdout", &self.stdout)
                .field("stderr", &self.stderr)
                .finish()
        }
    }

    /// A handle to a child process's standard input (stdin).
    ///
    /// This struct is used in the [`stdin`] field on [`Child`].
    ///
    /// When an instance of `ChildStdin` is [dropped], the `ChildStdin`'s underlying
    /// file handle will be closed. If the child process was blocked on input prior
    /// to being dropped, it will become unblocked after dropping.
    ///
    /// [`Child`]: struct.Child.html
    /// [`stdin`]: struct.Child.html#structfield.stdin
    /// [dropped]: ../ops/trait.Drop.html
    #[stable(feature = "process", since = "1.0.0")]
    pub struct ChildStdin {
        inner: AnonPipe,
    }

    #[stable(feature = "process", since = "1.0.0")]
    impl Write for ChildStdin {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            self.inner.write(buf)
        }

        fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
            self.inner.write_vectored(bufs)
        }

        fn is_write_vectored(&self) -> bool {
            self.inner.is_write_vectored()
        }

        fn flush(&mut self) -> io::Result<()> {
            Ok(())
        }
    }

    impl AsInner<AnonPipe> for ChildStdin {
        fn as_inner(&self) -> &AnonPipe {
            &self.inner
        }
    }

    impl IntoInner<AnonPipe> for ChildStdin {
        fn into_inner(self) -> AnonPipe {
            self.inner
        }
    }

    impl FromInner<AnonPipe> for ChildStdin {
        fn from_inner(pipe: AnonPipe) -> ChildStdin {
            ChildStdin { inner: pipe }
        }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for ChildStdin {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.pad("ChildStdin { .. }")
        }
    }

    /// A handle to a child process's standard output (stdout).
    ///
    /// This struct is used in the [`stdout`] field on [`Child`].
    ///
    /// When an instance of `ChildStdout` is [dropped], the `ChildStdout`'s
    /// underlying file handle will be closed.
    ///
    /// [`Child`]: struct.Child.html
    /// [`stdout`]: struct.Child.html#structfield.stdout
    /// [dropped]: ../ops/trait.Drop.html
    #[stable(feature = "process", since = "1.0.0")]
    pub struct ChildStdout {
        inner: AnonPipe,
    }

    #[stable(feature = "process", since = "1.0.0")]
    impl Read for ChildStdout {
        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
            self.inner.read(buf)
        }

        fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
            self.inner.read_vectored(bufs)
        }

        #[inline]
        fn is_read_vectored(&self) -> bool {
            self.inner.is_read_vectored()
        }

        #[inline]
        unsafe fn initializer(&self) -> Initializer {
            Initializer::nop()
        }
    }

    impl AsInner<AnonPipe> for ChildStdout {
        fn as_inner(&self) -> &AnonPipe {
            &self.inner
        }
    }

    impl IntoInner<AnonPipe> for ChildStdout {
        fn into_inner(self) -> AnonPipe {
            self.inner
        }
    }

    impl FromInner<AnonPipe> for ChildStdout {
        fn from_inner(pipe: AnonPipe) -> ChildStdout {
            ChildStdout { inner: pipe }
        }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for ChildStdout {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.pad("ChildStdout { .. }")
        }
    }

    /// A handle to a child process's stderr.
    ///
    /// This struct is used in the [`stderr`] field on [`Child`].
    ///
    /// When an instance of `ChildStderr` is [dropped], the `ChildStderr`'s
    /// underlying file handle will be closed.
    ///
    /// [`Child`]: struct.Child.html
    /// [`stderr`]: struct.Child.html#structfield.stderr
    /// [dropped]: ../ops/trait.Drop.html
    #[stable(feature = "process", since = "1.0.0")]
    pub struct ChildStderr {
        inner: AnonPipe,
    }

    #[stable(feature = "process", since = "1.0.0")]
    impl Read for ChildStderr {
        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
            self.inner.read(buf)
        }

        fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
            self.inner.read_vectored(bufs)
        }

        #[inline]
        fn is_read_vectored(&self) -> bool {
            self.inner.is_read_vectored()
        }

        #[inline]
        unsafe fn initializer(&self) -> Initializer {
            Initializer::nop()
        }
    }

    impl AsInner<AnonPipe> for ChildStderr {
        fn as_inner(&self) -> &AnonPipe {
            &self.inner
        }
    }

    impl IntoInner<AnonPipe> for ChildStderr {
        fn into_inner(self) -> AnonPipe {
            self.inner
        }
    }

    impl FromInner<AnonPipe> for ChildStderr {
        fn from_inner(pipe: AnonPipe) -> ChildStderr {
            ChildStderr { inner: pipe }
        }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for ChildStderr {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.pad("ChildStderr { .. }")
        }
    }

    /// A process builder, providing fine-grained control
    /// over how a new process should be spawned.
    ///
    /// A default configuration can be
    /// generated using `Command::new(program)`, where `program` gives a path to the
    /// program to be executed. Additional builder methods allow the configuration
    /// to be changed (for example, by adding arguments) prior to spawning:
    ///
    /// ```
    /// use std::process::Command;
    ///
    /// let output = if cfg!(target_os = "windows") {
    ///     Command::new("cmd")
    ///             .args(&["/C", "echo hello"])
    ///             .output()
    ///             .expect("failed to execute process")
    /// } else {
    ///     Command::new("sh")
    ///             .arg("-c")
    ///             .arg("echo hello")
    ///             .output()
    ///             .expect("failed to execute process")
    /// };
    ///
    /// let hello = output.stdout;
    /// ```
    ///
    /// `Command` can be reused to spawn multiple processes. The builder methods
    /// change the command without needing to immediately spawn the process.
    ///
    /// ```no_run
    /// use std::process::Command;
    ///
    /// let mut echo_hello = Command::new("sh");
    /// echo_hello.arg("-c")
    ///           .arg("echo hello");
    /// let hello_1 = echo_hello.output().expect("failed to execute process");
    /// let hello_2 = echo_hello.output().expect("failed to execute process");
    /// ```
    ///
    /// Similarly, you can call builder methods after spawning a process and then
    /// spawn a new process with the modified settings.
    ///
    /// ```no_run
    /// use std::process::Command;
    ///
    /// let mut list_dir = Command::new("ls");
    ///
    /// // Execute `ls` in the current directory of the program.
    /// list_dir.status().expect("process failed to execute");
    ///
    /// println!();
    ///
    /// // Change `ls` to execute in the root directory.
    /// list_dir.current_dir("/");
    ///
    /// // And then execute `ls` again but in the root directory.
    /// list_dir.status().expect("process failed to execute");
    /// ```
    #[stable(feature = "process", since = "1.0.0")]
    pub struct Command {
        inner: imp::Command,
    }

    impl Command {
        /// Constructs a new `Command` for launching the program at
        /// path `program`, with the following default configuration:
        ///
        /// * No arguments to the program
        /// * Inherit the current process's environment
        /// * Inherit the current process's working directory
        /// * Inherit stdin/stdout/stderr for `spawn` or `status`, but create pipes for `output`
        ///
        /// Builder methods are provided to change these defaults and
        /// otherwise configure the process.
        ///
        /// If `program` is not an absolute path, the `PATH` will be searched in
        /// an OS-defined way.
        ///
        /// The search path to be used may be controlled by setting the
        /// `PATH` environment variable on the Command,
        /// but this has some implementation limitations on Windows
        /// (see issue #37519).
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// Command::new("sh")
        ///         .spawn()
        ///         .expect("sh command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn new<S: AsRef<OsStr>>(program: S) -> Command {
            Command { inner: imp::Command::new(program.as_ref()) }
        }

        /// Adds an argument to pass to the program.
        ///
        /// Only one argument can be passed per use. So instead of:
        ///
        /// ```no_run
        /// # std::process::Command::new("sh")
        /// .arg("-C /path/to/repo")
        /// # ;
        /// ```
        ///
        /// usage would be:
        ///
        /// ```no_run
        /// # std::process::Command::new("sh")
        /// .arg("-C")
        /// .arg("/path/to/repo")
        /// # ;
        /// ```
        ///
        /// To pass multiple arguments see [`args`].
        ///
        /// [`args`]: #method.args
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// Command::new("ls")
        ///         .arg("-l")
        ///         .arg("-a")
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn arg<S: AsRef<OsStr>>(&mut self, arg: S) -> &mut Command {
            self.inner.arg(arg.as_ref());
            self
        }

        /// Adds multiple arguments to pass to the program.
        ///
        /// To pass a single argument see [`arg`].
        ///
        /// [`arg`]: #method.arg
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// Command::new("ls")
        ///         .args(&["-l", "-a"])
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn args<I, S>(&mut self, args: I) -> &mut Command
        where
            I: IntoIterator<Item = S>,
            S: AsRef<OsStr>,
        {
            for arg in args {
                self.arg(arg.as_ref());
            }
            self
        }

        /// Inserts or updates an environment variable mapping.
        ///
        /// Note that environment variable names are case-insensitive (but case-preserving) on Windows,
        /// and case-sensitive on all other platforms.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// Command::new("ls")
        ///         .env("PATH", "/bin")
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn env<K, V>(&mut self, key: K, val: V) -> &mut Command
        where
            K: AsRef<OsStr>,
            V: AsRef<OsStr>,
        {
            self.inner.env_mut().set(key.as_ref(), val.as_ref());
            self
        }

        /// Adds or updates multiple environment variable mappings.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        /// use std::env;
        /// use std::collections::HashMap;
        ///
        /// let filtered_env : HashMap<String, String> =
        ///     env::vars().filter(|&(ref k, _)|
        ///         k == "TERM" || k == "TZ" || k == "LANG" || k == "PATH"
        ///     ).collect();
        ///
        /// Command::new("printenv")
        ///         .stdin(Stdio::null())
        ///         .stdout(Stdio::inherit())
        ///         .env_clear()
        ///         .envs(&filtered_env)
        ///         .spawn()
        ///         .expect("printenv failed to start");
        /// ```
        #[stable(feature = "command_envs", since = "1.19.0")]
        pub fn envs<I, K, V>(&mut self, vars: I) -> &mut Command
        where
            I: IntoIterator<Item = (K, V)>,
            K: AsRef<OsStr>,
            V: AsRef<OsStr>,
        {
            for (ref key, ref val) in vars {
                self.inner.env_mut().set(key.as_ref(), val.as_ref());
            }
            self
        }

        /// Removes an environment variable mapping.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// Command::new("ls")
        ///         .env_remove("PATH")
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn env_remove<K: AsRef<OsStr>>(&mut self, key: K) -> &mut Command {
            self.inner.env_mut().remove(key.as_ref());
            self
        }

        /// Clears the entire environment map for the child process.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// Command::new("ls")
        ///         .env_clear()
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn env_clear(&mut self) -> &mut Command {
            self.inner.env_mut().clear();
            self
        }

        /// Sets the working directory for the child process.
        ///
        /// # Platform-specific behavior
        ///
        /// If the program path is relative (e.g., `"./script.sh"`), it's ambiguous
        /// whether it should be interpreted relative to the parent's working
        /// directory or relative to `current_dir`. The behavior in this case is
        /// platform specific and unstable, and it's recommended to use
        /// [`canonicalize`] to get an absolute program path instead.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// Command::new("ls")
        ///         .current_dir("/bin")
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        ///
        /// [`canonicalize`]: ../fs/fn.canonicalize.html
        #[stable(feature = "process", since = "1.0.0")]
        pub fn current_dir<P: AsRef<Path>>(&mut self, dir: P) -> &mut Command {
            self.inner.cwd(dir.as_ref().as_ref());
            self
        }

        /// Configuration for the child process's standard input (stdin) handle.
        ///
        /// Defaults to [`inherit`] when used with `spawn` or `status`, and
        /// defaults to [`piped`] when used with `output`.
        ///
        /// [`inherit`]: struct.Stdio.html#method.inherit
        /// [`piped`]: struct.Stdio.html#method.piped
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        ///
        /// Command::new("ls")
        ///         .stdin(Stdio::null())
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn stdin<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
            self.inner.stdin(cfg.into().0);
            self
        }

        /// Configuration for the child process's standard output (stdout) handle.
        ///
        /// Defaults to [`inherit`] when used with `spawn` or `status`, and
        /// defaults to [`piped`] when used with `output`.
        ///
        /// [`inherit`]: struct.Stdio.html#method.inherit
        /// [`piped`]: struct.Stdio.html#method.piped
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        ///
        /// Command::new("ls")
        ///         .stdout(Stdio::null())
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn stdout<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
            self.inner.stdout(cfg.into().0);
            self
        }

        /// Configuration for the child process's standard error (stderr) handle.
        ///
        /// Defaults to [`inherit`] when used with `spawn` or `status`, and
        /// defaults to [`piped`] when used with `output`.
        ///
        /// [`inherit`]: struct.Stdio.html#method.inherit
        /// [`piped`]: struct.Stdio.html#method.piped
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        ///
        /// Command::new("ls")
        ///         .stderr(Stdio::null())
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn stderr<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
            self.inner.stderr(cfg.into().0);
            self
        }

        /// Executes the command as a child process, returning a handle to it.
        ///
        /// By default, stdin, stdout and stderr are inherited from the parent.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// Command::new("ls")
        ///         .spawn()
        ///         .expect("ls command failed to start");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn spawn(&mut self) -> io::Result<Child> {
            self.inner.spawn(imp::Stdio::Inherit, true).map(Child::from_inner)
        }

        /// Executes the command as a child process, waiting for it to finish and
        /// collecting all of its output.
        ///
        /// By default, stdout and stderr are captured (and used to provide the
        /// resulting output). Stdin is not inherited from the parent and any
        /// attempt by the child process to read from the stdin stream will result
        /// in the stream immediately closing.
        ///
        /// # Examples
        ///
        /// ```should_panic
        /// use std::process::Command;
        /// use std::io::{self, Write};
        /// let output = Command::new("/bin/cat")
        ///                      .arg("file.txt")
        ///                      .output()
        ///                      .expect("failed to execute process");
        ///
        /// println!("status: {}", output.status);
        /// io::stdout().write_all(&output.stdout).unwrap();
        /// io::stderr().write_all(&output.stderr).unwrap();
        ///
        /// assert!(output.status.success());
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn output(&mut self) -> io::Result<Output> {
            self.inner
                .spawn(imp::Stdio::MakePipe, false)
                .map(Child::from_inner)
                .and_then(|p| p.wait_with_output())
        }

        /// Executes a command as a child process, waiting for it to finish and
        /// collecting its exit status.
        ///
        /// By default, stdin, stdout and stderr are inherited from the parent.
        ///
        /// # Examples
        ///
        /// ```should_panic
        /// use std::process::Command;
        ///
        /// let status = Command::new("/bin/cat")
        ///                      .arg("file.txt")
        ///                      .status()
        ///                      .expect("failed to execute process");
        ///
        /// println!("process exited with: {}", status);
        ///
        /// assert!(status.success());
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn status(&mut self) -> io::Result<ExitStatus> {
            self.inner
                .spawn(imp::Stdio::Inherit, true)
                .map(Child::from_inner)
                .and_then(|mut p| p.wait())
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl fmt::Debug for Command {
        /// Format the program and arguments of a Command for display. Any
        /// non-utf8 data is lossily converted using the utf8 replacement
        /// character.
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            self.inner.fmt(f)
        }
    }

    impl AsInner<imp::Command> for Command {
        fn as_inner(&self) -> &imp::Command {
            &self.inner
        }
    }

    impl AsInnerMut<imp::Command> for Command {
        fn as_inner_mut(&mut self) -> &mut imp::Command {
            &mut self.inner
        }
    }

    /// The output of a finished process.
    ///
    /// This is returned in a Result by either the [`output`] method of a
    /// [`Command`], or the [`wait_with_output`] method of a [`Child`]
    /// process.
    ///
    /// [`Command`]: struct.Command.html
    /// [`Child`]: struct.Child.html
    /// [`output`]: struct.Command.html#method.output
    /// [`wait_with_output`]: struct.Child.html#method.wait_with_output
    #[derive(PartialEq, Eq, Clone)]
    #[stable(feature = "process", since = "1.0.0")]
    pub struct Output {
        /// The status (exit code) of the process.
        #[stable(feature = "process", since = "1.0.0")]
        pub status: ExitStatus,
        /// The data that the process wrote to stdout.
        #[stable(feature = "process", since = "1.0.0")]
        pub stdout: Vec<u8>,
        /// The data that the process wrote to stderr.
        #[stable(feature = "process", since = "1.0.0")]
        pub stderr: Vec<u8>,
    }

    // If either stderr or stdout are valid utf8 strings it prints the valid
    // strings, otherwise it prints the byte sequence instead
    #[stable(feature = "process_output_debug", since = "1.7.0")]
    impl fmt::Debug for Output {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            let stdout_utf8 = str::from_utf8(&self.stdout);
            let stdout_debug: &dyn fmt::Debug = match stdout_utf8 {
                Ok(ref str) => str,
                Err(_) => &self.stdout,
            };

            let stderr_utf8 = str::from_utf8(&self.stderr);
            let stderr_debug: &dyn fmt::Debug = match stderr_utf8 {
                Ok(ref str) => str,
                Err(_) => &self.stderr,
            };

            fmt.debug_struct("Output")
                .field("status", &self.status)
                .field("stdout", stdout_debug)
                .field("stderr", stderr_debug)
                .finish()
        }
    }

    /// 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`].
    ///
    /// [`stdin`]: struct.Command.html#method.stdin
    /// [`stdout`]: struct.Command.html#method.stdout
    /// [`stderr`]: struct.Command.html#method.stderr
    /// [`Command`]: struct.Command.html
    #[stable(feature = "process", since = "1.0.0")]
    pub struct Stdio(imp::Stdio);

    impl Stdio {
        /// A new pipe should be arranged to connect the parent and child processes.
        ///
        /// # Examples
        ///
        /// With stdout:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        ///
        /// let output = Command::new("echo")
        ///     .arg("Hello, world!")
        ///     .stdout(Stdio::piped())
        ///     .output()
        ///     .expect("Failed to execute command");
        ///
        /// assert_eq!(String::from_utf8_lossy(&output.stdout), "Hello, world!\n");
        /// // Nothing echoed to console
        /// ```
        ///
        /// With stdin:
        ///
        /// ```no_run
        /// use std::io::Write;
        /// use std::process::{Command, Stdio};
        ///
        /// let mut child = Command::new("rev")
        ///     .stdin(Stdio::piped())
        ///     .stdout(Stdio::piped())
        ///     .spawn()
        ///     .expect("Failed to spawn child process");
        ///
        /// {
        ///     let stdin = child.stdin.as_mut().expect("Failed to open stdin");
        ///     stdin.write_all("Hello, world!".as_bytes()).expect("Failed to write to stdin");
        /// }
        ///
        /// let output = child.wait_with_output().expect("Failed to read stdout");
        /// assert_eq!(String::from_utf8_lossy(&output.stdout), "!dlrow ,olleH");
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn piped() -> Stdio {
            Stdio(imp::Stdio::MakePipe)
        }

        /// The child inherits from the corresponding parent descriptor.
        ///
        /// # Examples
        ///
        /// With stdout:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        ///
        /// let output = Command::new("echo")
        ///     .arg("Hello, world!")
        ///     .stdout(Stdio::inherit())
        ///     .output()
        ///     .expect("Failed to execute command");
        ///
        /// assert_eq!(String::from_utf8_lossy(&output.stdout), "");
        /// // "Hello, world!" echoed to console
        /// ```
        ///
        /// With stdin:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        /// use std::io::{self, Write};
        ///
        /// let output = Command::new("rev")
        ///     .stdin(Stdio::inherit())
        ///     .stdout(Stdio::piped())
        ///     .output()
        ///     .expect("Failed to execute command");
        ///
        /// print!("You piped in the reverse of: ");
        /// io::stdout().write_all(&output.stdout).unwrap();
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn inherit() -> Stdio {
            Stdio(imp::Stdio::Inherit)
        }

        /// This stream will be ignored. This is the equivalent of attaching the
        /// stream to `/dev/null`
        ///
        /// # Examples
        ///
        /// With stdout:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        ///
        /// let output = Command::new("echo")
        ///     .arg("Hello, world!")
        ///     .stdout(Stdio::null())
        ///     .output()
        ///     .expect("Failed to execute command");
        ///
        /// assert_eq!(String::from_utf8_lossy(&output.stdout), "");
        /// // Nothing echoed to console
        /// ```
        ///
        /// With stdin:
        ///
        /// ```no_run
        /// use std::process::{Command, Stdio};
        ///
        /// let output = Command::new("rev")
        ///     .stdin(Stdio::null())
        ///     .stdout(Stdio::piped())
        ///     .output()
        ///     .expect("Failed to execute command");
        ///
        /// assert_eq!(String::from_utf8_lossy(&output.stdout), "");
        /// // Ignores any piped-in input
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn null() -> Stdio {
            Stdio(imp::Stdio::Null)
        }
    }

    impl FromInner<imp::Stdio> for Stdio {
        fn from_inner(inner: imp::Stdio) -> Stdio {
            Stdio(inner)
        }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl fmt::Debug for Stdio {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.pad("Stdio { .. }")
        }
    }

    #[stable(feature = "stdio_from", since = "1.20.0")]
    impl From<ChildStdin> for Stdio {
        /// Converts a `ChildStdin` into a `Stdio`
        ///
        /// # Examples
        ///
        /// `ChildStdin` will be converted to `Stdio` using `Stdio::from` under the hood.
        ///
        /// ```rust,no_run
        /// use std::process::{Command, Stdio};
        ///
        /// let reverse = Command::new("rev")
        ///     .stdin(Stdio::piped())
        ///     .spawn()
        ///     .expect("failed reverse command");
        ///
        /// let _echo = Command::new("echo")
        ///     .arg("Hello, world!")
        ///     .stdout(reverse.stdin.unwrap()) // Converted into a Stdio here
        ///     .output()
        ///     .expect("failed echo command");
        ///
        /// // "!dlrow ,olleH" echoed to console
        /// ```
        fn from(child: ChildStdin) -> Stdio {
            Stdio::from_inner(child.into_inner().into())
        }
    }

    #[stable(feature = "stdio_from", since = "1.20.0")]
    impl From<ChildStdout> for Stdio {
        /// Converts a `ChildStdout` into a `Stdio`
        ///
        /// # Examples
        ///
        /// `ChildStdout` will be converted to `Stdio` using `Stdio::from` under the hood.
        ///
        /// ```rust,no_run
        /// use std::process::{Command, Stdio};
        ///
        /// let hello = Command::new("echo")
        ///     .arg("Hello, world!")
        ///     .stdout(Stdio::piped())
        ///     .spawn()
        ///     .expect("failed echo command");
        ///
        /// let reverse = Command::new("rev")
        ///     .stdin(hello.stdout.unwrap())  // Converted into a Stdio here
        ///     .output()
        ///     .expect("failed reverse command");
        ///
        /// assert_eq!(reverse.stdout, b"!dlrow ,olleH\n");
        /// ```
        fn from(child: ChildStdout) -> Stdio {
            Stdio::from_inner(child.into_inner().into())
        }
    }

    #[stable(feature = "stdio_from", since = "1.20.0")]
    impl From<ChildStderr> for Stdio {
        /// Converts a `ChildStderr` into a `Stdio`
        ///
        /// # Examples
        ///
        /// ```rust,no_run
        /// use std::process::{Command, Stdio};
        ///
        /// let reverse = Command::new("rev")
        ///     .arg("non_existing_file.txt")
        ///     .stderr(Stdio::piped())
        ///     .spawn()
        ///     .expect("failed reverse command");
        ///
        /// let cat = Command::new("cat")
        ///     .arg("-")
        ///     .stdin(reverse.stderr.unwrap()) // Converted into a Stdio here
        ///     .output()
        ///     .expect("failed echo command");
        ///
        /// assert_eq!(
        ///     String::from_utf8_lossy(&cat.stdout),
        ///     "rev: cannot open non_existing_file.txt: No such file or directory\n"
        /// );
        /// ```
        fn from(child: ChildStderr) -> Stdio {
            Stdio::from_inner(child.into_inner().into())
        }
    }

    #[stable(feature = "stdio_from", since = "1.20.0")]
    impl From<fs::File> for Stdio {
        /// Converts a `File` into a `Stdio`
        ///
        /// # Examples
        ///
        /// `File` will be converted to `Stdio` using `Stdio::from` under the hood.
        ///
        /// ```rust,no_run
        /// use std::fs::File;
        /// use std::process::Command;
        ///
        /// // With the `foo.txt` file containing `Hello, world!"
        /// let file = File::open("foo.txt").unwrap();
        ///
        /// let reverse = Command::new("rev")
        ///     .stdin(file)  // Implicit File conversion into a Stdio
        ///     .output()
        ///     .expect("failed reverse command");
        ///
        /// assert_eq!(reverse.stdout, b"!dlrow ,olleH");
        /// ```
        fn from(file: fs::File) -> Stdio {
            Stdio::from_inner(file.into_inner().into())
        }
    }

    /// Describes the result of a process after it has terminated.
    ///
    /// This `struct` is used to represent the exit status of a child process.
    /// Child processes are created via the [`Command`] struct and their exit
    /// status is exposed through the [`status`] method, or the [`wait`] method
    /// of a [`Child`] process.
    ///
    /// [`Command`]: struct.Command.html
    /// [`Child`]: struct.Child.html
    /// [`status`]: struct.Command.html#method.status
    /// [`wait`]: struct.Child.html#method.wait
    #[derive(PartialEq, Eq, Clone, Copy, Debug)]
    #[stable(feature = "process", since = "1.0.0")]
    pub struct ExitStatus(imp::ExitStatus);

    impl ExitStatus {
        /// Was termination successful? Signal termination is not considered a
        /// success, and success is defined as a zero exit status.
        ///
        /// # Examples
        ///
        /// ```rust,no_run
        /// use std::process::Command;
        ///
        /// let status = Command::new("mkdir")
        ///                      .arg("projects")
        ///                      .status()
        ///                      .expect("failed to execute mkdir");
        ///
        /// if status.success() {
        ///     println!("'projects/' directory created");
        /// } else {
        ///     println!("failed to create 'projects/' directory");
        /// }
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn success(&self) -> bool {
            self.0.success()
        }

        /// Returns the exit code of the process, if any.
        ///
        /// On Unix, this will return `None` if the process was terminated
        /// by a signal; `std::os::unix` provides an extension trait for
        /// extracting the signal and other details from the `ExitStatus`.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use std::process::Command;
        ///
        /// let status = Command::new("mkdir")
        ///                      .arg("projects")
        ///                      .status()
        ///                      .expect("failed to execute mkdir");
        ///
        /// match status.code() {
        ///     Some(code) => println!("Exited with status code: {}", code),
        ///     None       => println!("Process terminated by signal")
        /// }
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn code(&self) -> Option<i32> {
            self.0.code()
        }
    }

    impl AsInner<imp::ExitStatus> for ExitStatus {
        fn as_inner(&self) -> &imp::ExitStatus {
            &self.0
        }
    }

    impl FromInner<imp::ExitStatus> for ExitStatus {
        fn from_inner(s: imp::ExitStatus) -> ExitStatus {
            ExitStatus(s)
        }
    }

    #[stable(feature = "process", since = "1.0.0")]
    impl fmt::Display for ExitStatus {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            self.0.fmt(f)
        }
    }

    /// This type represents the status code a process can return to its
    /// parent under normal termination.
    ///
    /// Numeric values used in this type don't have portable meanings, and
    /// different platforms may mask different amounts of them.
    ///
    /// For the platform's canonical successful and unsuccessful codes, see
    /// the [`SUCCESS`] and [`FAILURE`] associated items.
    ///
    /// [`SUCCESS`]: #associatedconstant.SUCCESS
    /// [`FAILURE`]: #associatedconstant.FAILURE
    ///
    /// **Warning**: While various forms of this were discussed in [RFC #1937],
    /// it was ultimately cut from that RFC, and thus this type is more subject
    /// to change even than the usual unstable item churn.
    ///
    /// [RFC #1937]: https://github.com/rust-lang/rfcs/pull/1937
    #[derive(Clone, Copy, Debug)]
    #[unstable(feature = "process_exitcode_placeholder", issue = "48711")]
    pub struct ExitCode(imp::ExitCode);

    #[unstable(feature = "process_exitcode_placeholder", issue = "48711")]
    impl ExitCode {
        /// The canonical ExitCode for successful termination on this platform.
        ///
        /// Note that a `()`-returning `main` implicitly results in a successful
        /// termination, so there's no need to return this from `main` unless
        /// you're also returning other possible codes.
        #[unstable(feature = "process_exitcode_placeholder", issue = "48711")]
        pub const SUCCESS: ExitCode = ExitCode(imp::ExitCode::SUCCESS);

        /// The canonical ExitCode for unsuccessful termination on this platform.
        ///
        /// If you're only returning this and `SUCCESS` from `main`, consider
        /// instead returning `Err(_)` and `Ok(())` respectively, which will
        /// return the same codes (but will also `eprintln!` the error).
        #[unstable(feature = "process_exitcode_placeholder", issue = "48711")]
        pub const FAILURE: ExitCode = ExitCode(imp::ExitCode::FAILURE);
    }

    impl Child {
        /// 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,
        /// especially the [`Other`] kind might change to more specific kinds in the future.
        ///
        /// This is equivalent to sending a SIGKILL on Unix platforms.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// 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");
        /// }
        /// ```
        ///
        /// [`ErrorKind`]: ../io/enum.ErrorKind.html
        /// [`InvalidInput`]: ../io/enum.ErrorKind.html#variant.InvalidInput
        /// [`Other`]: ../io/enum.ErrorKind.html#variant.Other
        #[stable(feature = "process", since = "1.0.0")]
        pub fn kill(&mut self) -> io::Result<()> {
            self.handle.kill()
        }

        /// Returns the OS-assigned process identifier associated with this child.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```no_run
        /// 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");
        /// }
        /// ```
        #[stable(feature = "process_id", since = "1.3.0")]
        pub fn id(&self) -> u32 {
            self.handle.id()
        }

        /// 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:
        ///
        /// ```no_run
        /// 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");
        /// }
        /// ```
        #[stable(feature = "process", since = "1.0.0")]
        pub fn wait(&mut self) -> io::Result<ExitStatus> {
            drop(self.stdin.take());
            self.handle.wait().map(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:
        ///
        /// ```no_run
        /// 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),
        /// }
        /// ```
        #[stable(feature = "process_try_wait", since = "1.18.0")]
        pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
            Ok(self.handle.try_wait()?.map(ExitStatus))
        }

        /// 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
        ///
        /// ```should_panic
        /// 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());
        /// ```
        ///
        #[stable(feature = "process", since = "1.0.0")]
        pub fn wait_with_output(mut self) -> io::Result<Output> {
            drop(self.stdin.take());

            let (mut stdout, mut stderr) = (Vec::new(), Vec::new());
            match (self.stdout.take(), self.stderr.take()) {
                (None, None) => {}
                (Some(mut out), None) => {
                    let res = out.read_to_end(&mut stdout);
                    res.unwrap();
                }
                (None, Some(mut err)) => {
                    let res = err.read_to_end(&mut stderr);
                    res.unwrap();
                }
                (Some(out), Some(err)) => {
                    let res = read2(out.inner, &mut stdout, err.inner, &mut stderr);
                    res.unwrap();
                }
            }

            let status = self.wait()?;
            Ok(Output { status, stdout, stderr })
        }
    }

    /// Terminates the current process with the specified exit code.
    ///
    /// This function will never return and will immediately terminate the current
    /// process. The exit code is passed through to the underlying OS and will be
    /// available for consumption by another process.
    ///
    /// Note that because this function never returns, and that it terminates the
    /// process, no destructors on the current stack or any other thread's stack
    /// will be run. If a clean shutdown is needed it is recommended to only call
    /// this function at a known point where there are no more destructors left
    /// to run.
    ///
    /// ## Platform-specific behavior
    ///
    /// **Unix**: On Unix-like platforms, it is unlikely that all 32 bits of `exit`
    /// will be visible to a parent process inspecting the exit code. On most
    /// Unix-like platforms, only the eight least-significant bits are considered.
    ///
    /// # Examples
    ///
    /// Due to this function’s behavior regarding destructors, a conventional way
    /// to use the function is to extract the actual computation to another
    /// function and compute the exit code from its return value:
    ///
    /// ```
    /// fn run_app() -> Result<(), ()> {
    ///     // Application logic here
    ///     Ok(())
    /// }
    ///
    /// fn main() {
    ///     std::process::exit(match run_app() {
    ///         Ok(_) => 0,
    ///         Err(err) => {
    ///             eprintln!("error: {:?}", err);
    ///             1
    ///         }
    ///     });
    /// }
    /// ```
    ///
    /// Due to [platform-specific behavior], the exit code for this example will be
    /// `0` on Linux, but `256` on Windows:
    ///
    /// ```no_run
    /// use std::process;
    ///
    /// process::exit(0x0100);
    /// ```
    ///
    /// [platform-specific behavior]: #platform-specific-behavior
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn exit(code: i32) -> ! {
        crate::sys_common::cleanup();
        crate::sys::os::exit(code)
    }

    /// Terminates the process in an abnormal fashion.
    ///
    /// The function will never return and will immediately terminate the current
    /// process in a platform specific "abnormal" manner.
    ///
    /// Note that because this function never returns, and that it terminates the
    /// process, no destructors on the current stack or any other thread's stack
    /// will be run.
    ///
    /// This is in contrast to the default behaviour of [`panic!`] which unwinds
    /// the current thread's stack and calls all destructors.
    /// When `panic="abort"` is set, either as an argument to `rustc` or in a
    /// crate's Cargo.toml, [`panic!`] and `abort` are similar. However,
    /// [`panic!`] will still call the [panic hook] while `abort` will not.
    ///
    /// If a clean shutdown is needed it is recommended to only call
    /// this function at a known point where there are no more destructors left
    /// to run.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::process;
    ///
    /// fn main() {
    ///     println!("aborting");
    ///
    ///     process::abort();
    ///
    ///     // execution never gets here
    /// }
    /// ```
    ///
    /// The `abort` function terminates the process, so the destructor will not
    /// get run on the example below:
    ///
    /// ```no_run
    /// use std::process;
    ///
    /// struct HasDrop;
    ///
    /// impl Drop for HasDrop {
    ///     fn drop(&mut self) {
    ///         println!("This will never be printed!");
    ///     }
    /// }
    ///
    /// fn main() {
    ///     let _x = HasDrop;
    ///     process::abort();
    ///     // the destructor implemented for HasDrop will never get run
    /// }
    /// ```
    ///
    /// [`panic!`]: ../../std/macro.panic.html
    /// [panic hook]: ../../std/panic/fn.set_hook.html
    #[stable(feature = "process_abort", since = "1.17.0")]
    pub fn abort() -> ! {
        crate::sys::abort_internal();
    }

    /// Returns the OS-assigned process identifier associated with this process.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use std::process;
    ///
    /// println!("My pid is {}", process::id());
    /// ```
    ///
    ///
    #[stable(feature = "getpid", since = "1.26.0")]
    pub fn id() -> u32 {
        crate::sys::os::getpid()
    }

    /// A trait for implementing arbitrary return types in the `main` function.
    ///
    /// The C-main function only supports to return integers as return type.
    /// So, every type implementing the `Termination` trait has to be converted
    /// to an integer.
    ///
    /// The default implementations are returning `libc::EXIT_SUCCESS` to indicate
    /// a successful execution. In case of a failure, `libc::EXIT_FAILURE` is returned.
    #[cfg_attr(not(test), lang = "termination")]
    #[unstable(feature = "termination_trait_lib", issue = "43301")]
    #[rustc_on_unimplemented(
        message = "`main` has invalid return type `{Self}`",
        label = "`main` can only return types that implement `{Termination}`"
    )]
    pub trait Termination {
        /// Is called to get the representation of the value as status code.
        /// This status code is returned to the operating system.
        fn report(self) -> i32;
    }

    #[unstable(feature = "termination_trait_lib", issue = "43301")]
    impl Termination for () {
        #[inline]
        fn report(self) -> i32 {
            ExitCode::SUCCESS.report()
        }
    }

    #[unstable(feature = "termination_trait_lib", issue = "43301")]
    impl<E: fmt::Debug> Termination for Result<(), E> {
        fn report(self) -> i32 {
            match self {
                Ok(()) => ().report(),
                Err(err) => Err::<!, _>(err).report(),
            }
        }
    }

    #[unstable(feature = "termination_trait_lib", issue = "43301")]
    impl Termination for ! {
        fn report(self) -> i32 {
            self
        }
    }

    #[unstable(feature = "termination_trait_lib", issue = "43301")]
    impl<E: fmt::Debug> Termination for Result<!, E> {
        fn report(self) -> i32 {
            let Err(err) = self;
            eprintln!("Error: {:?}", err);
            ExitCode::FAILURE.report()
        }
    }

    #[unstable(feature = "termination_trait_lib", issue = "43301")]
    impl Termination for ExitCode {
        #[inline]
        fn report(self) -> i32 {
            self.0.as_i32()
        }
    }

    #[cfg(all(test, not(any(target_os = "cloudabi", target_os = "emscripten", target_env = "sgx"))))]
    mod tests {
        use crate::io::prelude::*;

        use super::{Command, Output, Stdio};
        use crate::io::ErrorKind;
        use crate::str;

        // FIXME(#10380) these tests should not all be ignored on android.

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn smoke() {
            let p = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "exit 0"]).spawn()
            } else {
                Command::new("true").spawn()
            };
            assert!(p.is_ok());
            let mut p = p.unwrap();
            assert!(p.wait().unwrap().success());
        }

        #[test]
        #[cfg_attr(target_os = "android", ignore)]
        fn smoke_failure() {
            match Command::new("if-this-is-a-binary-then-the-world-has-ended").spawn() {
                Ok(..) => panic!(),
                Err(..) => {}
            }
        }

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn exit_reported_right() {
            let p = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "exit 1"]).spawn()
            } else {
                Command::new("false").spawn()
            };
            assert!(p.is_ok());
            let mut p = p.unwrap();
            assert!(p.wait().unwrap().code() == Some(1));
            drop(p.wait());
        }

        #[test]
        #[cfg(unix)]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn signal_reported_right() {
            use crate::os::unix::process::ExitStatusExt;

            let mut p =
                Command::new("/bin/sh").arg("-c").arg("read a").stdin(Stdio::piped()).spawn().unwrap();
            p.kill().unwrap();
            match p.wait().unwrap().signal() {
                Some(9) => {}
                result => panic!("not terminated by signal 9 (instead, {:?})", result),
            }
        }

        pub fn run_output(mut cmd: Command) -> String {
            let p = cmd.spawn();
            assert!(p.is_ok());
            let mut p = p.unwrap();
            assert!(p.stdout.is_some());
            let mut ret = String::new();
            p.stdout.as_mut().unwrap().read_to_string(&mut ret).unwrap();
            assert!(p.wait().unwrap().success());
            return ret;
        }

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn stdout_works() {
            if cfg!(target_os = "windows") {
                let mut cmd = Command::new("cmd");
                cmd.args(&["/C", "echo foobar"]).stdout(Stdio::piped());
                assert_eq!(run_output(cmd), "foobar\r\n");
            } else {
                let mut cmd = Command::new("echo");
                cmd.arg("foobar").stdout(Stdio::piped());
                assert_eq!(run_output(cmd), "foobar\n");
            }
        }

        #[test]
        #[cfg_attr(any(windows, target_os = "android", target_os = "vxworks"), ignore)]
        fn set_current_dir_works() {
            let mut cmd = Command::new("/bin/sh");
            cmd.arg("-c").arg("pwd").current_dir("/").stdout(Stdio::piped());
            assert_eq!(run_output(cmd), "/\n");
        }

        #[test]
        #[cfg_attr(any(windows, target_os = "android", target_os = "vxworks"), ignore)]
        fn stdin_works() {
            let mut p = Command::new("/bin/sh")
                .arg("-c")
                .arg("read line; echo $line")
                .stdin(Stdio::piped())
                .stdout(Stdio::piped())
                .spawn()
                .unwrap();
            p.stdin.as_mut().unwrap().write("foobar".as_bytes()).unwrap();
            drop(p.stdin.take());
            let mut out = String::new();
            p.stdout.as_mut().unwrap().read_to_string(&mut out).unwrap();
            assert!(p.wait().unwrap().success());
            assert_eq!(out, "foobar\n");
        }

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn test_process_status() {
            let mut status = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "exit 1"]).status().unwrap()
            } else {
                Command::new("false").status().unwrap()
            };
            assert!(status.code() == Some(1));

            status = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "exit 0"]).status().unwrap()
            } else {
                Command::new("true").status().unwrap()
            };
            assert!(status.success());
        }

        #[test]
        fn test_process_output_fail_to_start() {
            match Command::new("/no-binary-by-this-name-should-exist").output() {
                Err(e) => assert_eq!(e.kind(), ErrorKind::NotFound),
                Ok(..) => panic!(),
            }
        }

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn test_process_output_output() {
            let Output { status, stdout, stderr } = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "echo hello"]).output().unwrap()
            } else {
                Command::new("echo").arg("hello").output().unwrap()
            };
            let output_str = str::from_utf8(&stdout).unwrap();

            assert!(status.success());
            assert_eq!(output_str.trim().to_string(), "hello");
            assert_eq!(stderr, Vec::new());
        }

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn test_process_output_error() {
            let Output { status, stdout, stderr } = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "mkdir ."]).output().unwrap()
            } else {
                Command::new("mkdir").arg("./").output().unwrap()
            };

            assert!(status.code() == Some(1));
            assert_eq!(stdout, Vec::new());
            assert!(!stderr.is_empty());
        }

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn test_finish_once() {
            let mut prog = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "exit 1"]).spawn().unwrap()
            } else {
                Command::new("false").spawn().unwrap()
            };
            assert!(prog.wait().unwrap().code() == Some(1));
        }

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn test_finish_twice() {
            let mut prog = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "exit 1"]).spawn().unwrap()
            } else {
                Command::new("false").spawn().unwrap()
            };
            assert!(prog.wait().unwrap().code() == Some(1));
            assert!(prog.wait().unwrap().code() == Some(1));
        }

        #[test]
        #[cfg_attr(any(target_os = "vxworks", target_os = "android"), ignore)]
        fn test_wait_with_output_once() {
            let prog = if cfg!(target_os = "windows") {
                Command::new("cmd").args(&["/C", "echo hello"]).stdout(Stdio::piped()).spawn().unwrap()
            } else {
                Command::new("echo").arg("hello").stdout(Stdio::piped()).spawn().unwrap()
            };

            let Output { status, stdout, stderr } = prog.wait_with_output().unwrap();
            let output_str = str::from_utf8(&stdout).unwrap();

            assert!(status.success());
            assert_eq!(output_str.trim().to_string(), "hello");
            assert_eq!(stderr, Vec::new());
        }

        #[cfg(all(unix, not(target_os = "android")))]
        pub fn env_cmd() -> Command {
            Command::new("env")
        }
        #[cfg(target_os = "android")]
        pub fn env_cmd() -> Command {
            let mut cmd = Command::new("/system/bin/sh");
            cmd.arg("-c").arg("set");
            cmd
        }

        #[cfg(windows)]
        pub fn env_cmd() -> Command {
            let mut cmd = Command::new("cmd");
            cmd.arg("/c").arg("set");
            cmd
        }

        #[test]
        #[cfg_attr(target_os = "vxworks", ignore)]
        fn test_override_env() {
            use crate::env;

            // In some build environments (such as chrooted Nix builds), `env` can
            // only be found in the explicitly-provided PATH env variable, not in
            // default places such as /bin or /usr/bin. So we need to pass through
            // PATH to our sub-process.
            let mut cmd = env_cmd();
            cmd.env_clear().env("RUN_TEST_NEW_ENV", "123");
            if let Some(p) = env::var_os("PATH") {
                cmd.env("PATH", &p);
            }
            let result = cmd.output().unwrap();
            let output = String::from_utf8_lossy(&result.stdout).to_string();

            assert!(
                output.contains("RUN_TEST_NEW_ENV=123"),
                "didn't find RUN_TEST_NEW_ENV inside of:\n\n{}",
                output
            );
        }

        #[test]
        #[cfg_attr(target_os = "vxworks", ignore)]
        fn test_add_to_env() {
            let result = env_cmd().env("RUN_TEST_NEW_ENV", "123").output().unwrap();
            let output = String::from_utf8_lossy(&result.stdout).to_string();

            assert!(
                output.contains("RUN_TEST_NEW_ENV=123"),
                "didn't find RUN_TEST_NEW_ENV inside of:\n\n{}",
                output
            );
        }

        #[test]
        #[cfg_attr(target_os = "vxworks", ignore)]
        fn test_capture_env_at_spawn() {
            use crate::env;

            let mut cmd = env_cmd();
            cmd.env("RUN_TEST_NEW_ENV1", "123");

            // This variable will not be present if the environment has already
            // been captured above.
            env::set_var("RUN_TEST_NEW_ENV2", "456");
            let result = cmd.output().unwrap();
            env::remove_var("RUN_TEST_NEW_ENV2");

            let output = String::from_utf8_lossy(&result.stdout).to_string();

            assert!(
                output.contains("RUN_TEST_NEW_ENV1=123"),
                "didn't find RUN_TEST_NEW_ENV1 inside of:\n\n{}",
                output
            );
            assert!(
                output.contains("RUN_TEST_NEW_ENV2=456"),
                "didn't find RUN_TEST_NEW_ENV2 inside of:\n\n{}",
                output
            );
        }

        // Regression tests for #30858.
        #[test]
        fn test_interior_nul_in_progname_is_error() {
            match Command::new("has-some-\0\0s-inside").spawn() {
                Err(e) => assert_eq!(e.kind(), ErrorKind::InvalidInput),
                Ok(_) => panic!(),
            }
        }

        #[test]
        fn test_interior_nul_in_arg_is_error() {
            match Command::new("echo").arg("has-some-\0\0s-inside").spawn() {
                Err(e) => assert_eq!(e.kind(), ErrorKind::InvalidInput),
                Ok(_) => panic!(),
            }
        }

        #[test]
        fn test_interior_nul_in_args_is_error() {
            match Command::new("echo").args(&["has-some-\0\0s-inside"]).spawn() {
                Err(e) => assert_eq!(e.kind(), ErrorKind::InvalidInput),
                Ok(_) => panic!(),
            }
        }

        #[test]
        fn test_interior_nul_in_current_dir_is_error() {
            match Command::new("echo").current_dir("has-some-\0\0s-inside").spawn() {
                Err(e) => assert_eq!(e.kind(), ErrorKind::InvalidInput),
                Ok(_) => panic!(),
            }
        }

        // Regression tests for #30862.
        #[test]
        #[cfg_attr(target_os = "vxworks", ignore)]
        fn test_interior_nul_in_env_key_is_error() {
            match env_cmd().env("has-some-\0\0s-inside", "value").spawn() {
                Err(e) => assert_eq!(e.kind(), ErrorKind::InvalidInput),
                Ok(_) => panic!(),
            }
        }

        #[test]
        #[cfg_attr(target_os = "vxworks", ignore)]
        fn test_interior_nul_in_env_value_is_error() {
            match env_cmd().env("key", "has-some-\0\0s-inside").spawn() {
                Err(e) => assert_eq!(e.kind(), ErrorKind::InvalidInput),
                Ok(_) => panic!(),
            }
        }

        /// Tests that process creation flags work by debugging a process.
        /// Other creation flags make it hard or impossible to detect
        /// behavioral changes in the process.
        #[test]
        #[cfg(windows)]
        fn test_creation_flags() {
            use crate::os::windows::process::CommandExt;
            use crate::sys::c::{BOOL, DWORD, INFINITE};
            #[repr(C, packed)]
            struct DEBUG_EVENT {
                pub event_code: DWORD,
                pub process_id: DWORD,
                pub thread_id: DWORD,
                // This is a union in the real struct, but we don't
                // need this data for the purposes of this test.
                pub _junk: [u8; 164],
            }

            extern "system" {
                fn WaitForDebugEvent(lpDebugEvent: *mut DEBUG_EVENT, dwMilliseconds: DWORD) -> BOOL;
                fn ContinueDebugEvent(
                    dwProcessId: DWORD,
                    dwThreadId: DWORD,
                    dwContinueStatus: DWORD,
                ) -> BOOL;
            }

            const DEBUG_PROCESS: DWORD = 1;
            const EXIT_PROCESS_DEBUG_EVENT: DWORD = 5;
            const DBG_EXCEPTION_NOT_HANDLED: DWORD = 0x80010001;

            let mut child = Command::new("cmd")
                .creation_flags(DEBUG_PROCESS)
                .stdin(Stdio::piped())
                .spawn()
                .unwrap();
            child.stdin.take().unwrap().write_all(b"exit\r\n").unwrap();
            let mut events = 0;
            let mut event = DEBUG_EVENT { event_code: 0, process_id: 0, thread_id: 0, _junk: [0; 164] };
            loop {
                if unsafe { WaitForDebugEvent(&mut event as *mut DEBUG_EVENT, INFINITE) } == 0 {
                    panic!("WaitForDebugEvent failed!");
                }
                events += 1;

                if event.event_code == EXIT_PROCESS_DEBUG_EVENT {
                    break;
                }

                if unsafe {
                    ContinueDebugEvent(event.process_id, event.thread_id, DBG_EXCEPTION_NOT_HANDLED)
                } == 0
                {
                    panic!("ContinueDebugEvent failed!");
                }
            }
            assert!(events > 0);
        }

        #[test]
        fn test_command_implements_send_sync() {
            fn take_send_sync_type<T: Send + Sync>(_: T) {}
            take_send_sync_type(Command::new(""))
        }
    }