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    //! Inspection and manipulation of the process's environment.
    //!
    //! This module contains functions to inspect various aspects such as
    //! environment variables, process arguments, the current directory, and various
    //! other important directories.
    //!
    //! There are several functions and structs in this module that have a
    //! counterpart ending in `os`. Those ending in `os` will return an [`OsString`]
    //! and those without will return a [`String`].

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

    #[cfg(test)]
    mod tests;

    use crate::error::Error;
    use crate::ffi::{OsStr, OsString};
    use crate::fmt;
    use crate::io;
    use crate::path::{Path, PathBuf};
    use crate::sys;
    use crate::sys::os as os_imp;

    /// Returns the current working directory as a [`PathBuf`].
    ///
    /// # Errors
    ///
    /// Returns an [`Err`] if the current working directory value is invalid.
    /// Possible cases:
    ///
    /// * Current directory does not exist.
    /// * There are insufficient permissions to access the current directory.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let path = env::current_dir()?;
    ///     println!("The current directory is {}", path.display());
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn current_dir() -> io::Result<PathBuf> {
        os_imp::getcwd()
    }

    /// Changes the current working directory to the specified path.
    ///
    /// Returns an [`Err`] if the operation fails.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    /// use std::path::Path;
    ///
    /// let root = Path::new("/");
    /// assert!(env::set_current_dir(&root).is_ok());
    /// println!("Successfully changed working directory to {}!", root.display());
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn set_current_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
        os_imp::chdir(path.as_ref())
    }

    /// An iterator over a snapshot of the environment variables of this process.
    ///
    /// This structure is created by [`env::vars()`]. See its documentation for more.
    ///
    /// [`env::vars()`]: vars
    #[stable(feature = "env", since = "1.0.0")]
    pub struct Vars {
        inner: VarsOs,
    }

    /// An iterator over a snapshot of the environment variables of this process.
    ///
    /// This structure is created by [`env::vars_os()`]. See its documentation for more.
    ///
    /// [`env::vars_os()`]: vars_os
    #[stable(feature = "env", since = "1.0.0")]
    pub struct VarsOs {
        inner: os_imp::Env,
    }

    /// Returns an iterator of (variable, value) pairs of strings, for all the
    /// environment variables of the current process.
    ///
    /// The returned iterator contains a snapshot of the process's environment
    /// variables at the time of this invocation. Modifications to environment
    /// variables afterwards will not be reflected in the returned iterator.
    ///
    /// # Panics
    ///
    /// While iterating, the returned iterator will panic if any key or value in the
    /// environment is not valid unicode. If this is not desired, consider using
    /// [`env::vars_os()`].
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // We will iterate through the references to the element returned by
    /// // env::vars();
    /// for (key, value) in env::vars() {
    ///     println!("{}: {}", key, value);
    /// }
    /// ```
    ///
    /// [`env::vars_os()`]: vars_os
    #[stable(feature = "env", since = "1.0.0")]
    pub fn vars() -> Vars {
        Vars { inner: vars_os() }
    }

    /// Returns an iterator of (variable, value) pairs of OS strings, for all the
    /// environment variables of the current process.
    ///
    /// The returned iterator contains a snapshot of the process's environment
    /// variables at the time of this invocation. Modifications to environment
    /// variables afterwards will not be reflected in the returned iterator.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // We will iterate through the references to the element returned by
    /// // env::vars_os();
    /// for (key, value) in env::vars_os() {
    ///     println!("{:?}: {:?}", key, value);
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn vars_os() -> VarsOs {
        VarsOs { inner: os_imp::env() }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl Iterator for Vars {
        type Item = (String, String);
        fn next(&mut self) -> Option<(String, String)> {
            self.inner.next().map(|(a, b)| (a.into_string().unwrap(), b.into_string().unwrap()))
        }
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.inner.size_hint()
        }
    }

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

    #[stable(feature = "env", since = "1.0.0")]
    impl Iterator for VarsOs {
        type Item = (OsString, OsString);
        fn next(&mut self) -> Option<(OsString, OsString)> {
            self.inner.next()
        }
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.inner.size_hint()
        }
    }

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

    /// Fetches the environment variable `key` from the current process.
    ///
    /// # Errors
    ///
    /// * Environment variable is not present
    /// * Environment variable is not valid unicode
    ///
    /// # Panics
    ///
    /// This function may panic if `key` is empty, contains an ASCII equals sign
    /// `'='` or the NUL character `'\0'`, or when the value contains the NUL
    /// character.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "HOME";
    /// match env::var(key) {
    ///     Ok(val) => println!("{}: {:?}", key, val),
    ///     Err(e) => println!("couldn't interpret {}: {}", key, e),
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn var<K: AsRef<OsStr>>(key: K) -> Result<String, VarError> {
        _var(key.as_ref())
    }

    fn _var(key: &OsStr) -> Result<String, VarError> {
        match var_os(key) {
            Some(s) => s.into_string().map_err(VarError::NotUnicode),
            None => Err(VarError::NotPresent),
        }
    }

    /// Fetches the environment variable `key` from the current process, returning
    /// [`None`] if the variable isn't set.
    ///
    /// # Panics
    ///
    /// This function may panic if `key` is empty, contains an ASCII equals sign
    /// `'='` or the NUL character `'\0'`, or when the value contains the NUL
    /// character.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "HOME";
    /// match env::var_os(key) {
    ///     Some(val) => println!("{}: {:?}", key, val),
    ///     None => println!("{} is not defined in the environment.", key)
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn var_os<K: AsRef<OsStr>>(key: K) -> Option<OsString> {
        _var_os(key.as_ref())
    }

    fn _var_os(key: &OsStr) -> Option<OsString> {
        os_imp::getenv(key)
            .unwrap_or_else(|e| panic!("failed to get environment variable `{:?}`: {}", key, e))
    }

    /// The error type for operations interacting with environment variables.
    /// Possibly returned from [`env::var()`].
    ///
    /// [`env::var()`]: var
    #[derive(Debug, PartialEq, Eq, Clone)]
    #[stable(feature = "env", since = "1.0.0")]
    pub enum VarError {
        /// The specified environment variable was not present in the current
        /// process's environment.
        #[stable(feature = "env", since = "1.0.0")]
        NotPresent,

        /// The specified environment variable was found, but it did not contain
        /// valid unicode data. The found data is returned as a payload of this
        /// variant.
        #[stable(feature = "env", since = "1.0.0")]
        NotUnicode(#[stable(feature = "env", since = "1.0.0")] OsString),
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl fmt::Display for VarError {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match *self {
                VarError::NotPresent => write!(f, "environment variable not found"),
                VarError::NotUnicode(ref s) => {
                    write!(f, "environment variable was not valid unicode: {:?}", s)
                }
            }
        }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl Error for VarError {
        #[allow(deprecated)]
        fn description(&self) -> &str {
            match *self {
                VarError::NotPresent => "environment variable not found",
                VarError::NotUnicode(..) => "environment variable was not valid unicode",
            }
        }
    }

    /// Sets the environment variable `k` to the value `v` for the currently running
    /// process.
    ///
    /// Note that while concurrent access to environment variables is safe in Rust,
    /// some platforms only expose inherently unsafe non-threadsafe APIs for
    /// inspecting the environment. As a result, extra care needs to be taken when
    /// auditing calls to unsafe external FFI functions to ensure that any external
    /// environment accesses are properly synchronized with accesses in Rust.
    ///
    /// Discussion of this unsafety on Unix may be found in:
    ///
    ///  - [Austin Group Bugzilla](http://austingroupbugs.net/view.php?id=188)
    ///  - [GNU C library Bugzilla](https://sourceware.org/bugzilla/show_bug.cgi?id=15607#c2)
    ///
    /// # Panics
    ///
    /// This function may panic if `key` is empty, contains an ASCII equals sign
    /// `'='` or the NUL character `'\0'`, or when the value contains the NUL
    /// character.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "KEY";
    /// env::set_var(key, "VALUE");
    /// assert_eq!(env::var(key), Ok("VALUE".to_string()));
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn set_var<K: AsRef<OsStr>, V: AsRef<OsStr>>(k: K, v: V) {
        _set_var(k.as_ref(), v.as_ref())
    }

    fn _set_var(k: &OsStr, v: &OsStr) {
        os_imp::setenv(k, v).unwrap_or_else(|e| {
            panic!("failed to set environment variable `{:?}` to `{:?}`: {}", k, v, e)
        })
    }

    /// Removes an environment variable from the environment of the currently running process.
    ///
    /// Note that while concurrent access to environment variables is safe in Rust,
    /// some platforms only expose inherently unsafe non-threadsafe APIs for
    /// inspecting the environment. As a result extra care needs to be taken when
    /// auditing calls to unsafe external FFI functions to ensure that any external
    /// environment accesses are properly synchronized with accesses in Rust.
    ///
    /// Discussion of this unsafety on Unix may be found in:
    ///
    ///  - [Austin Group Bugzilla](http://austingroupbugs.net/view.php?id=188)
    ///  - [GNU C library Bugzilla](https://sourceware.org/bugzilla/show_bug.cgi?id=15607#c2)
    ///
    /// # Panics
    ///
    /// This function may panic if `key` is empty, contains an ASCII equals sign
    /// `'='` or the NUL character `'\0'`, or when the value contains the NUL
    /// character.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "KEY";
    /// env::set_var(key, "VALUE");
    /// assert_eq!(env::var(key), Ok("VALUE".to_string()));
    ///
    /// env::remove_var(key);
    /// assert!(env::var(key).is_err());
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn remove_var<K: AsRef<OsStr>>(k: K) {
        _remove_var(k.as_ref())
    }

    fn _remove_var(k: &OsStr) {
        os_imp::unsetenv(k)
            .unwrap_or_else(|e| panic!("failed to remove environment variable `{:?}`: {}", k, e))
    }

    /// An iterator that splits an environment variable into paths according to
    /// platform-specific conventions.
    ///
    /// The iterator element type is [`PathBuf`].
    ///
    /// This structure is created by [`env::split_paths()`]. See its
    /// documentation for more.
    ///
    /// [`env::split_paths()`]: split_paths
    #[stable(feature = "env", since = "1.0.0")]
    pub struct SplitPaths<'a> {
        inner: os_imp::SplitPaths<'a>,
    }

    /// Parses input according to platform conventions for the `PATH`
    /// environment variable.
    ///
    /// Returns an iterator over the paths contained in `unparsed`. The iterator
    /// element type is [`PathBuf`].
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// let key = "PATH";
    /// match env::var_os(key) {
    ///     Some(paths) => {
    ///         for path in env::split_paths(&paths) {
    ///             println!("'{}'", path.display());
    ///         }
    ///     }
    ///     None => println!("{} is not defined in the environment.", key)
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn split_paths<T: AsRef<OsStr> + ?Sized>(unparsed: &T) -> SplitPaths<'_> {
        SplitPaths { inner: os_imp::split_paths(unparsed.as_ref()) }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl<'a> Iterator for SplitPaths<'a> {
        type Item = PathBuf;
        fn next(&mut self) -> Option<PathBuf> {
            self.inner.next()
        }
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.inner.size_hint()
        }
    }

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

    /// The error type for operations on the `PATH` variable. Possibly returned from
    /// [`env::join_paths()`].
    ///
    /// [`env::join_paths()`]: join_paths
    #[derive(Debug)]
    #[stable(feature = "env", since = "1.0.0")]
    pub struct JoinPathsError {
        inner: os_imp::JoinPathsError,
    }

    /// Joins a collection of [`Path`]s appropriately for the `PATH`
    /// environment variable.
    ///
    /// # Errors
    ///
    /// Returns an [`Err`] (containing an error message) if one of the input
    /// [`Path`]s contains an invalid character for constructing the `PATH`
    /// variable (a double quote on Windows or a colon on Unix).
    ///
    /// # Examples
    ///
    /// Joining paths on a Unix-like platform:
    ///
    /// ```
    /// use std::env;
    /// use std::ffi::OsString;
    /// use std::path::Path;
    ///
    /// fn main() -> Result<(), env::JoinPathsError> {
    /// # if cfg!(unix) {
    ///     let paths = [Path::new("/bin"), Path::new("/usr/bin")];
    ///     let path_os_string = env::join_paths(paths.iter())?;
    ///     assert_eq!(path_os_string, OsString::from("/bin:/usr/bin"));
    /// # }
    ///     Ok(())
    /// }
    /// ```
    ///
    /// Joining a path containing a colon on a Unix-like platform results in an
    /// error:
    ///
    /// ```
    /// # if cfg!(unix) {
    /// use std::env;
    /// use std::path::Path;
    ///
    /// let paths = [Path::new("/bin"), Path::new("/usr/bi:n")];
    /// assert!(env::join_paths(paths.iter()).is_err());
    /// # }
    /// ```
    ///
    /// Using `env::join_paths()` with [`env::split_paths()`] to append an item to
    /// the `PATH` environment variable:
    ///
    /// ```
    /// use std::env;
    /// use std::path::PathBuf;
    ///
    /// fn main() -> Result<(), env::JoinPathsError> {
    ///     if let Some(path) = env::var_os("PATH") {
    ///         let mut paths = env::split_paths(&path).collect::<Vec<_>>();
    ///         paths.push(PathBuf::from("/home/xyz/bin"));
    ///         let new_path = env::join_paths(paths)?;
    ///         env::set_var("PATH", &new_path);
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    ///
    /// [`env::split_paths()`]: split_paths
    #[stable(feature = "env", since = "1.0.0")]
    pub fn join_paths<I, T>(paths: I) -> Result<OsString, JoinPathsError>
    where
        I: IntoIterator<Item = T>,
        T: AsRef<OsStr>,
    {
        os_imp::join_paths(paths.into_iter()).map_err(|e| JoinPathsError { inner: e })
    }

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

    #[stable(feature = "env", since = "1.0.0")]
    impl Error for JoinPathsError {
        #[allow(deprecated, deprecated_in_future)]
        fn description(&self) -> &str {
            self.inner.description()
        }
    }

    /// Returns the path of the current user's home directory if known.
    ///
    /// # Unix
    ///
    /// - Returns the value of the 'HOME' environment variable if it is set
    ///   (including to an empty string).
    /// - Otherwise, it tries to determine the home directory by invoking the `getpwuid_r` function
    ///   using the UID of the current user. An empty home directory field returned from the
    ///   `getpwuid_r` function is considered to be a valid value.
    /// - Returns `None` if the current user has no entry in the /etc/passwd file.
    ///
    /// # Windows
    ///
    /// - Returns the value of the 'HOME' environment variable if it is set
    ///   (including to an empty string).
    /// - Otherwise, returns the value of the 'USERPROFILE' environment variable if it is set
    ///   (including to an empty string).
    /// - If both do not exist, [`GetUserProfileDirectory`][msdn] is used to return the path.
    ///
    /// [msdn]: https://docs.microsoft.com/en-us/windows/win32/api/userenv/nf-userenv-getuserprofiledirectorya
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// match env::home_dir() {
    ///     Some(path) => println!("Your home directory, probably: {}", path.display()),
    ///     None => println!("Impossible to get your home dir!"),
    /// }
    /// ```
    #[rustc_deprecated(
        since = "1.29.0",
        reason = "This function's behavior is unexpected and probably not what you want. \
                  Consider using a crate from crates.io instead."
    )]
    #[stable(feature = "env", since = "1.0.0")]
    pub fn home_dir() -> Option<PathBuf> {
        os_imp::home_dir()
    }

    /// Returns the path of a temporary directory.
    ///
    /// # Unix
    ///
    /// Returns the value of the `TMPDIR` environment variable if it is
    /// set, otherwise for non-Android it returns `/tmp`. If Android, since there
    /// is no global temporary folder (it is usually allocated per-app), it returns
    /// `/data/local/tmp`.
    ///
    /// # Windows
    ///
    /// Returns the value of, in order, the `TMP`, `TEMP`,
    /// `USERPROFILE` environment variable if any are set and not the empty
    /// string. Otherwise, `temp_dir` returns the path of the Windows directory.
    /// This behavior is identical to that of [`GetTempPath`][msdn], which this
    /// function uses internally.
    ///
    /// [msdn]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppatha
    ///
    /// ```no_run
    /// use std::env;
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut dir = env::temp_dir();
    ///     dir.push("foo.txt");
    ///
    ///     let f = File::create(dir)?;
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn temp_dir() -> PathBuf {
        os_imp::temp_dir()
    }

    /// Returns the full filesystem path of the current running executable.
    ///
    /// # Platform-specific behavior
    ///
    /// If the executable was invoked through a symbolic link, some platforms will
    /// return the path of the symbolic link and other platforms will return the
    /// path of the symbolic link’s target.
    ///
    /// # Errors
    ///
    /// Acquiring the path of the current executable is a platform-specific operation
    /// that can fail for a good number of reasons. Some errors can include, but not
    /// be limited to, filesystem operations failing or general syscall failures.
    ///
    /// # Security
    ///
    /// The output of this function should not be used in anything that might have
    /// security implications. For example:
    ///
    /// ```
    /// fn main() {
    ///     println!("{:?}", std::env::current_exe());
    /// }
    /// ```
    ///
    /// On Linux systems, if this is compiled as `foo`:
    ///
    /// ```bash
    /// $ rustc foo.rs
    /// $ ./foo
    /// Ok("/home/alex/foo")
    /// ```
    ///
    /// And you make a hard link of the program:
    ///
    /// ```bash
    /// $ ln foo bar
    /// ```
    ///
    /// When you run it, you won’t get the path of the original executable, you’ll
    /// get the path of the hard link:
    ///
    /// ```bash
    /// $ ./bar
    /// Ok("/home/alex/bar")
    /// ```
    ///
    /// This sort of behavior has been known to [lead to privilege escalation] when
    /// used incorrectly.
    ///
    /// [lead to privilege escalation]: https://securityvulns.com/Wdocument183.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// match env::current_exe() {
    ///     Ok(exe_path) => println!("Path of this executable is: {}",
    ///                              exe_path.display()),
    ///     Err(e) => println!("failed to get current exe path: {}", e),
    /// };
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn current_exe() -> io::Result<PathBuf> {
        os_imp::current_exe()
    }

    /// An iterator over the arguments of a process, yielding a [`String`] value for
    /// each argument.
    ///
    /// This struct is created by [`env::args()`]. See its documentation
    /// for more.
    ///
    /// The first element is traditionally the path of the executable, but it can be
    /// set to arbitrary text, and may not even exist. This means this property
    /// should not be relied upon for security purposes.
    ///
    /// [`env::args()`]: args
    #[stable(feature = "env", since = "1.0.0")]
    pub struct Args {
        inner: ArgsOs,
    }

    /// An iterator over the arguments of a process, yielding an [`OsString`] value
    /// for each argument.
    ///
    /// This struct is created by [`env::args_os()`]. See its documentation
    /// for more.
    ///
    /// The first element is traditionally the path of the executable, but it can be
    /// set to arbitrary text, and may not even exist. This means this property
    /// should not be relied upon for security purposes.
    ///
    /// [`env::args_os()`]: args_os
    #[stable(feature = "env", since = "1.0.0")]
    pub struct ArgsOs {
        inner: sys::args::Args,
    }

    /// Returns the arguments that this program was started with (normally passed
    /// via the command line).
    ///
    /// The first element is traditionally the path of the executable, but it can be
    /// set to arbitrary text, and may not even exist. This means this property should
    /// not be relied upon for security purposes.
    ///
    /// On Unix systems the shell usually expands unquoted arguments with glob patterns
    /// (such as `*` and `?`). On Windows this is not done, and such arguments are
    /// passed as-is.
    ///
    /// On glibc Linux systems, arguments are retrieved by placing a function in `.init_array`.
    /// Glibc passes `argc`, `argv`, and `envp` to functions in `.init_array`, as a non-standard
    /// extension. This allows `std::env::args` to work even in a `cdylib` or `staticlib`, as it
    /// does on macOS and Windows.
    ///
    /// # Panics
    ///
    /// The returned iterator will panic during iteration if any argument to the
    /// process is not valid unicode. If this is not desired,
    /// use the [`args_os`] function instead.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // Prints each argument on a separate line
    /// for argument in env::args() {
    ///     println!("{}", argument);
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn args() -> Args {
        Args { inner: args_os() }
    }

    /// Returns the arguments which this program was started with (normally passed
    /// via the command line).
    ///
    /// The first element is traditionally the path of the executable, but it can be
    /// set to arbitrary text, and it may not even exist, so this property should
    /// not be relied upon for security purposes.
    ///
    /// On glibc Linux systems, arguments are retrieved by placing a function in ".init_array".
    /// Glibc passes argc, argv, and envp to functions in ".init_array", as a non-standard extension.
    /// This allows `std::env::args` to work even in a `cdylib` or `staticlib`, as it does on macOS
    /// and Windows.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::env;
    ///
    /// // Prints each argument on a separate line
    /// for argument in env::args_os() {
    ///     println!("{:?}", argument);
    /// }
    /// ```
    #[stable(feature = "env", since = "1.0.0")]
    pub fn args_os() -> ArgsOs {
        ArgsOs { inner: sys::args::args() }
    }

    #[stable(feature = "env_unimpl_send_sync", since = "1.26.0")]
    impl !Send for Args {}

    #[stable(feature = "env_unimpl_send_sync", since = "1.26.0")]
    impl !Sync for Args {}

    #[stable(feature = "env", since = "1.0.0")]
    impl Iterator for Args {
        type Item = String;
        fn next(&mut self) -> Option<String> {
            self.inner.next().map(|s| s.into_string().unwrap())
        }
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.inner.size_hint()
        }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl ExactSizeIterator for Args {
        fn len(&self) -> usize {
            self.inner.len()
        }
        fn is_empty(&self) -> bool {
            self.inner.is_empty()
        }
    }

    #[stable(feature = "env_iterators", since = "1.12.0")]
    impl DoubleEndedIterator for Args {
        fn next_back(&mut self) -> Option<String> {
            self.inner.next_back().map(|s| s.into_string().unwrap())
        }
    }

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

    #[stable(feature = "env_unimpl_send_sync", since = "1.26.0")]
    impl !Send for ArgsOs {}

    #[stable(feature = "env_unimpl_send_sync", since = "1.26.0")]
    impl !Sync for ArgsOs {}

    #[stable(feature = "env", since = "1.0.0")]
    impl Iterator for ArgsOs {
        type Item = OsString;
        fn next(&mut self) -> Option<OsString> {
            self.inner.next()
        }
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.inner.size_hint()
        }
    }

    #[stable(feature = "env", since = "1.0.0")]
    impl ExactSizeIterator for ArgsOs {
        fn len(&self) -> usize {
            self.inner.len()
        }
        fn is_empty(&self) -> bool {
            self.inner.is_empty()
        }
    }

    #[stable(feature = "env_iterators", since = "1.12.0")]
    impl DoubleEndedIterator for ArgsOs {
        fn next_back(&mut self) -> Option<OsString> {
            self.inner.next_back()
        }
    }

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

    /// Constants associated with the current target
    #[stable(feature = "env", since = "1.0.0")]
    pub mod consts {
        use crate::sys::env::os;

        /// A string describing the architecture of the CPU that is currently
        /// in use.
        ///
        /// Some possible values:
        ///
        /// - x86
        /// - x86_64
        /// - arm
        /// - aarch64
        /// - mips
        /// - mips64
        /// - powerpc
        /// - powerpc64
        /// - riscv64
        /// - s390x
        /// - sparc64
        #[stable(feature = "env", since = "1.0.0")]
        pub const ARCH: &str = env!("STD_ENV_ARCH");

        /// The family of the operating system. Example value is `unix`.
        ///
        /// Some possible values:
        ///
        /// - unix
        /// - windows
        #[stable(feature = "env", since = "1.0.0")]
        pub const FAMILY: &str = os::FAMILY;

        /// A string describing the specific operating system in use.
        /// Example value is `linux`.
        ///
        /// Some possible values:
        ///
        /// - linux
        /// - macos
        /// - ios
        /// - freebsd
        /// - dragonfly
        /// - netbsd
        /// - openbsd
        /// - solaris
        /// - android
        /// - windows
        #[stable(feature = "env", since = "1.0.0")]
        pub const OS: &str = os::OS;

        /// Specifies the filename prefix used for shared libraries on this
        /// platform. Example value is `lib`.
        ///
        /// Some possible values:
        ///
        /// - lib
        /// - `""` (an empty string)
        #[stable(feature = "env", since = "1.0.0")]
        pub const DLL_PREFIX: &str = os::DLL_PREFIX;

        /// Specifies the filename suffix used for shared libraries on this
        /// platform. Example value is `.so`.
        ///
        /// Some possible values:
        ///
        /// - .so
        /// - .dylib
        /// - .dll
        #[stable(feature = "env", since = "1.0.0")]
        pub const DLL_SUFFIX: &str = os::DLL_SUFFIX;

        /// Specifies the file extension used for shared libraries on this
        /// platform that goes after the dot. Example value is `so`.
        ///
        /// Some possible values:
        ///
        /// - so
        /// - dylib
        /// - dll
        #[stable(feature = "env", since = "1.0.0")]
        pub const DLL_EXTENSION: &str = os::DLL_EXTENSION;

        /// Specifies the filename suffix used for executable binaries on this
        /// platform. Example value is `.exe`.
        ///
        /// Some possible values:
        ///
        /// - .exe
        /// - .nexe
        /// - .pexe
        /// - `""` (an empty string)
        #[stable(feature = "env", since = "1.0.0")]
        pub const EXE_SUFFIX: &str = os::EXE_SUFFIX;

        /// Specifies the file extension, if any, used for executable binaries
        /// on this platform. Example value is `exe`.
        ///
        /// Some possible values:
        ///
        /// - exe
        /// - `""` (an empty string)
        #[stable(feature = "env", since = "1.0.0")]
        pub const EXE_EXTENSION: &str = os::EXE_EXTENSION;
    }