Struct Command

pub struct Command { /* private fields */ }

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.

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.

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");

Implementations

impl Command

pub fn new<S: AsRef<OsStr>>(program: S) -> 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).

Platform-specific behavior

Note on Windows: For executable files with the .exe extension, it can be omitted when specifying the program for this Command. However, if the file has a different extension, a filename including the extension needs to be provided, otherwise the file won’t be found.

Examples

use std::process::Command;

Command::new("sh")
    .spawn()
    .expect("sh command failed to start");

Caveats

Command::new is only intended to accept the path of the program. If you pass a program path along with arguments like Command::new("ls -l").spawn(), it will try to search for ls -l literally. The arguments need to be passed separately, such as via arg or args.

use std::process::Command;

Command::new("ls")
    .arg("-l") // arg passed separately
    .spawn()
    .expect("ls command failed to start");

pub fn arg<S: AsRef<OsStr>>(&mut self, arg: S) -> &mut Command

Adds an argument to pass to the program.

Only one argument can be passed per use. So instead of:

.arg("-C /path/to/repo")

usage would be:

.arg("-C")
.arg("/path/to/repo")

To pass multiple arguments see args.

Note that the argument is not passed through a shell, but given literally to the program. This means that shell syntax like quotes, escaped characters, word splitting, glob patterns, variable substitution, etc. have no effect.

On Windows, use caution with untrusted inputs. Most applications use the standard convention for decoding arguments passed to them. These are safe to use with arg. However, some applications such as cmd.exe and .bat files use a non-standard way of decoding arguments. They are therefore vulnerable to malicious input.

In the case of cmd.exe this is especially important because a malicious argument can potentially run arbitrary shell commands.

See Windows argument splitting for more details or raw_arg for manually implementing non-standard argument encoding.

Examples

use std::process::Command;

Command::new("ls")
    .arg("-l")
    .arg("-a")
    .spawn()
    .expect("ls command failed to start");

pub fn args<I, S>(&mut self, args: I) -> &mut Command

where I: IntoIterator<Item = S>, S: AsRef<OsStr>,

Adds multiple arguments to pass to the program.

To pass a single argument see arg.

Note that the arguments are not passed through a shell, but given literally to the program. This means that shell syntax like quotes, escaped characters, word splitting, glob patterns, variable substitution, etc. have no effect.

On Windows, use caution with untrusted inputs. Most applications use the standard convention for decoding arguments passed to them. These are safe to use with arg. However, some applications such as cmd.exe and .bat files use a non-standard way of decoding arguments. They are therefore vulnerable to malicious input.

In the case of cmd.exe this is especially important because a malicious argument can potentially run arbitrary shell commands.

See Windows argument splitting for more details or raw_arg for manually implementing non-standard argument encoding.

Examples

use std::process::Command;

Command::new("ls")
    .args(["-l", "-a"])
    .spawn()
    .expect("ls command failed to start");

pub fn env<K, V>(&mut self, key: K, val: V) -> &mut Command

where K: AsRef<OsStr>, V: AsRef<OsStr>,

Inserts or updates an explicit environment variable mapping.

This method allows you to add an environment variable mapping to the spawned process or overwrite a previously set value. You can use Command::envs to set multiple environment variables simultaneously.

Child processes will inherit environment variables from their parent process by default. Environment variables explicitly set using Command::env take precedence over inherited variables. You can disable environment variable inheritance entirely using Command::env_clear or for a single key using Command::env_remove.

Note that environment variable names are case-insensitive (but case-preserving) on Windows and case-sensitive on all other platforms.

Examples

use std::process::Command;

Command::new("ls")
    .env("PATH", "/bin")
    .spawn()
    .expect("ls command failed to start");

pub fn envs<I, K, V>(&mut self, vars: I) -> &mut Command

where I: IntoIterator<Item = (K, V)>, K: AsRef<OsStr>, V: AsRef<OsStr>,

Inserts or updates multiple explicit environment variable mappings.

This method allows you to add multiple environment variable mappings to the spawned process or overwrite previously set values. You can use Command::env to set a single environment variable.

Child processes will inherit environment variables from their parent process by default. Environment variables explicitly set using Command::envs take precedence over inherited variables. You can disable environment variable inheritance entirely using Command::env_clear or for a single key using Command::env_remove.

Note that environment variable names are case-insensitive (but case-preserving) on Windows and case-sensitive on all other platforms.

Examples

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");

pub fn env_remove<K: AsRef<OsStr>>(&mut self, key: K) -> &mut Command

Removes an explicitly set environment variable and prevents inheriting it from a parent process.

This method will remove the explicit value of an environment variable set via Command::env or Command::envs. In addition, it will prevent the spawned child process from inheriting that environment variable from its parent process.

After calling Command::env_remove, the value associated with its key from Command::get_envs will be None.

To clear all explicitly set environment variables and disable all environment variable inheritance, you can use Command::env_clear.

Examples

use std::process::Command;

Command::new("ls")
    .env_remove("PATH")
    .spawn()
    .expect("ls command failed to start");

pub fn env_clear(&mut self) -> &mut Command

Clears all explicitly set environment variables and prevents inheriting any parent process environment variables.

This method will remove all explicitly added environment variables set via Command::env or Command::envs. In addition, it will prevent the spawned child process from inheriting any environment variable from its parent process.

After calling Command::env_clear, the iterator from Command::get_envs will be empty.

You can use Command::env_remove to clear a single mapping.

Examples

use std::process::Command;

Command::new("ls")
    .env_clear()
    .spawn()
    .expect("ls command failed to start");

pub fn current_dir<P: AsRef<Path>>(&mut self, dir: P) -> &mut Command

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

use std::process::Command;

Command::new("ls")
    .current_dir("/bin")
    .spawn()
    .expect("ls command failed to start");

pub fn stdin<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command

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.

Examples

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

Command::new("ls")
    .stdin(Stdio::null())
    .spawn()
    .expect("ls command failed to start");

pub fn stdout<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command

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.

Examples

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

Command::new("ls")
    .stdout(Stdio::null())
    .spawn()
    .expect("ls command failed to start");

pub fn stderr<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command

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.

Examples

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

Command::new("ls")
    .stderr(Stdio::null())
    .spawn()
    .expect("ls command failed to start");

pub fn spawn(&mut self) -> Result<Child>

Executes the command as a child process, returning a handle to it.

By default, stdin, stdout and stderr are inherited from the parent.

Examples

use std::process::Command;

Command::new("ls")
    .spawn()
    .expect("ls command failed to start");

pub fn output(&mut self) -> Result<Output>

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

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());

pub fn status(&mut self) -> Result<ExitStatus>

Executes a command as a child process, waiting for it to finish and collecting its status.

By default, stdin, stdout and stderr are inherited from the parent.

Examples

use std::process::Command;

let status = Command::new("/bin/cat")
    .arg("file.txt")
    .status()
    .expect("failed to execute process");

println!("process finished with: {status}");

assert!(status.success());

pub fn get_program(&self) -> &OsStr

Returns the path to the program that was given to Command::new.

Examples

use std::process::Command;

let cmd = Command::new("echo");
assert_eq!(cmd.get_program(), "echo");

pub fn get_args(&self) -> CommandArgs<'_>

Returns an iterator of the arguments that will be passed to the program.

This does not include the path to the program as the first argument; it only includes the arguments specified with Command::arg and Command::args.

Examples

use std::ffi::OsStr;
use std::process::Command;

let mut cmd = Command::new("echo");
cmd.arg("first").arg("second");
let args: Vec<&OsStr> = cmd.get_args().collect();
assert_eq!(args, &["first", "second"]);

pub fn get_envs(&self) -> CommandEnvs<'_>

Returns an iterator of the environment variables explicitly set for the child process.

Environment variables explicitly set using Command::env, Command::envs, and Command::env_remove can be retrieved with this method.

Note that this output does not include environment variables inherited from the parent process.

Each element is a tuple key/value pair (&OsStr, Option<&OsStr>). A None value indicates its key was explicitly removed via Command::env_remove. The associated key for the None value will no longer inherit from its parent process.

An empty iterator can indicate that no explicit mappings were added or that Command::env_clear was called. After calling Command::env_clear, the child process will not inherit any environment variables from its parent process.

Examples

use std::ffi::OsStr;
use std::process::Command;

let mut cmd = Command::new("ls");
cmd.env("TERM", "dumb").env_remove("TZ");
let envs: Vec<(&OsStr, Option<&OsStr>)> = cmd.get_envs().collect();
assert_eq!(envs, &[
    (OsStr::new("TERM"), Some(OsStr::new("dumb"))),
    (OsStr::new("TZ"), None)
]);

pub fn get_current_dir(&self) -> Option<&Path>

Returns the working directory for the child process.

This returns None if the working directory will not be changed.

Examples

use std::path::Path;
use std::process::Command;

let mut cmd = Command::new("ls");
assert_eq!(cmd.get_current_dir(), None);
cmd.current_dir("/bin");
assert_eq!(cmd.get_current_dir(), Some(Path::new("/bin")));

Trait Implementations

impl CommandExt for Command

Available on Unix only.

fn uid(&mut self, id: u32) -> &mut Command

Sets the child process’s user ID. This translates to a setuid call in the child process. Failure in the setuid call will cause the spawn to fail.

fn gid(&mut self, id: u32) -> &mut Command

Similar to uid, but sets the group ID of the child process. This has the same semantics as the uid field.

fn groups(&mut self, groups: &[u32]) -> &mut Command

🔬This is a nightly-only experimental API. (setgroups #90747)

Sets the supplementary group IDs for the calling process. Translates to a setgroups call in the child process.

unsafe fn pre_exec<F>(&mut self, f: F) -> &mut Command

where F: FnMut() -> Result<()> + Send + Sync + 'static,

Schedules a closure to be run just before the exec function is invoked.

fn exec(&mut self) -> Error

Performs all the required setup by this Command, followed by calling the execvp syscall.

fn arg0<S>(&mut self, arg: S) -> &mut Command

where S: AsRef<OsStr>,

Set executable argument

fn process_group(&mut self, pgroup: i32) -> &mut Command

Sets the process group ID (PGID) of the child process. Equivalent to a setpgid call in the child process, but may be more efficient.

unsafe fn before_exec<F>(&mut self, f: F) -> &mut Command

where F: FnMut() -> Result<()> + Send + Sync + 'static,

👎Deprecated since 1.37.0: should be unsafe, use pre_exec instead

Schedules a closure to be run just before the exec function is invoked.

impl CommandExt for Command

Available on Linux only.

fn create_pidfd(&mut self, val: bool) -> &mut Command

🔬This is a nightly-only experimental API. (linux_pidfd #82971)

Sets whether a PidFd should be created for the Child spawned by this Command. By default, no pidfd will be created.

impl CommandExt for Command

Available on Windows only.

fn creation_flags(&mut self, flags: u32) -> &mut Command

Sets the process creation flags to be passed to CreateProcess.

fn show_window(&mut self, cmd_show: u16) -> &mut Command

🔬This is a nightly-only experimental API. (windows_process_extensions_show_window #127544)

Sets the field wShowWindow of STARTUPINFO that is passed to CreateProcess. Allowed values are the ones listed in https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-showwindow

fn force_quotes(&mut self, enabled: bool) -> &mut Command

🔬This is a nightly-only experimental API. (windows_process_extensions_force_quotes #82227)

Forces all arguments to be wrapped in quote (") characters.

fn raw_arg<S: AsRef<OsStr>>(&mut self, raw_text: S) -> &mut Command

Append literal text to the command line without any quoting or escaping.

fn async_pipes(&mut self, always_async: bool) -> &mut Command

🔬This is a nightly-only experimental API. (windows_process_extensions_async_pipes #98289)

When process::Command creates pipes, request that our side is always async.

unsafe fn raw_attribute<T: Copy + Send + Sync + 'static>( &mut self, attribute: usize, value: T, ) -> &mut Command

🔬This is a nightly-only experimental API. (windows_process_extensions_raw_attribute #114854)

Set a raw attribute on the command, providing extended configuration options for Windows processes.

impl Debug for Command

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

Format the program and arguments of a Command for display. Any non-utf8 data is lossily converted using the utf8 replacement character.

The default format approximates a shell invocation of the program along with its arguments. It does not include most of the other command properties. The output is not guaranteed to work (e.g. due to lack of shell-escaping or differences in path resolution). On some platforms you can use the alternate syntax to show more fields.

Note that the debug implementation is platform-specific.