### Get Shell Executable

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Retrieves the shell executable path, defaulting to cmd.exe on Windows if ComSpec is not set.

```rust
pub fn get_shell(&self) -> String {
        let exe: OsString = self
            .get_env("ComSpec")
            .unwrap_or(OsStr::new("cmd.exe"))
            .into();
        exe.into_string()
            .unwrap_or_else(|_| "%CompSpec%".to_string())
    }
```

--------------------------------

### Get Current Directory as Wide String

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Retrieves the current working directory or home directory as a null-terminated wide string for Windows API compatibility.

```rust
pub(crate) fn current_directory(&self) -> Option<Vec<u16>> {
        let home: Option<&OsStr> = self
            .get_env("USERPROFILE")
            .filter(|path| Path::new(path).is_dir());
        let cwd: Option<&OsStr> = self.cwd.as_deref().filter(|path| Path::new(path).is_dir());
        let dir: Option<&OsStr> = cwd.or(home);

        dir.map(|dir| {
            let mut wide = vec![];

            if Path::new(dir).is_relative() {
                if let Ok(ccwd) = std::env::current_dir() {
                    wide.extend(ccwd.join(dir).as_os_str().encode_wide());
                } else {
                    wide.extend(dir.encode_wide());
                }
            } else {
                wide.extend(dir.encode_wide());
            }

            wide.push(0);
            wide
        })
    }
```

--------------------------------

### Unix Path Relative Check

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Checks if a given path starts with current directory or parent directory components on Unix systems.

```rust
#[cfg(unix)]
/// Returns true if the path begins with `./` or `../`
fn is_cwd_relative_path<P: AsRef<Path>>(p: P) -> bool {
    matches!(
        p.as_ref().components().next(),
        Some(Component::CurDir | Component::ParentDir)
    )
}
```

--------------------------------

### Controlling Terminal Configuration

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Methods to get and set whether the pty should act as the controlling terminal, useful for containerized environments.

```rust
    pub fn set_controlling_tty(&mut self, controlling_tty: bool) {
        self.controlling_tty = controlling_tty;
    }

    pub fn get_controlling_tty(&self) -> bool {
        self.controlling_tty
    }
```

--------------------------------

### UnixPtySystem::openpty

Source: https://docs.rs/portable-pty/latest/portable_pty/unix/struct.UnixPtySystem.html

Creates a new PTY instance with the specified window size, returning a master and slave pair.

```APIDOC
## fn openpty(&self, size: PtySize) -> Result<PtyPair>

### Description
Creates a new PTY instance with the window size set to the specified dimensions. Returns a (master, slave) Pty pair. The master side is used to drive the slave side.

### Parameters
- **size** (PtySize) - Required - The initial window dimensions for the PTY.

### Returns
- **Result<PtyPair>** - A result containing the PTY pair on success, or an error if the operation fails.
```

--------------------------------

### CommandBuilder Initialization Methods

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Methods for creating new instances of CommandBuilder with different initial states.

```rust
impl CommandBuilder {
    /// Create a new builder instance with argv[0] set to the specified
    /// program.
    pub fn new<S: AsRef<OsStr>>(program: S) -> Self {
        Self {
            args: vec![program.as_ref().to_owned()],
            envs: get_base_env(),
            cwd: None,
            #[cfg(unix)]
            umask: None,
            controlling_tty: true,
        }
    }

    /// Create a new builder instance from a pre-built argument vector
    pub fn from_argv(args: Vec<OsString>) -> Self {
        Self {
            args,
            envs: get_base_env(),
            cwd: None,
            #[cfg(unix)]
            umask: None,
            controlling_tty: true,
        }
    }

    /// Create a new builder instance that will run some idea of a default
    /// program.  Such a builder will panic if `arg` is called on it.
    pub fn new_default_prog() -> Self {
        Self {
            args: vec![],
            envs: get_base_env(),
            cwd: None,
            #[cfg(unix)]
            umask: None,
            controlling_tty: true,
        }
    }
```

--------------------------------

### Spawn a shell in a pseudo-terminal

Source: https://docs.rs/portable-pty/latest/index.html

Demonstrates initializing a native pty system, opening a pty pair, spawning a bash shell, and interacting with the master end.

```rust
use portable_pty::{CommandBuilder, PtySize, native_pty_system, PtySystem};
use anyhow::Error;

// Use the native pty implementation for the system
let pty_system = native_pty_system();

// Create a new pty
let mut pair = pty_system.openpty(PtySize {
    rows: 24,
    cols: 80,
    // Not all systems support pixel_width, pixel_height,
    // but it is good practice to set it to something
    // that matches the size of the selected font.  That
    // is more complex than can be shown here in this
    // brief example though!
    pixel_width: 0,
    pixel_height: 0,
})?;

// Spawn a shell into the pty
let cmd = CommandBuilder::new("bash");
let child = pair.slave.spawn_command(cmd)?;

// Read and parse output from the pty with reader
let mut reader = pair.master.try_clone_reader()?;

// Send data to the pty by writing to the master
writeln!(pair.master.take_writer()?, "ls -l\r\n")?;
```

--------------------------------

### NativePtySystem::openpty

Source: https://docs.rs/portable-pty/latest/portable_pty/type.NativePtySystem.html

Creates a new PTY instance with the specified window dimensions, returning a master and slave pair.

```APIDOC
## fn openpty(&self, size: PtySize) -> Result<PtyPair>

### Description
Creates a new PTY instance with the window size set to the specified dimensions. The master side is used to drive the slave side.

### Parameters
- **size** (PtySize) - Required - The initial dimensions for the PTY window.

### Returns
- **Result<PtyPair>** - A Result containing a (master, slave) PtyPair on success, or an error if the PTY could not be created.
```

--------------------------------

### Initialize base environment map

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Collects current environment variables into a BTreeMap, ensuring platform-specific defaults like SHELL are populated on Unix.

```rust
fn get_base_env() -> BTreeMap<OsString, EnvEntry> {
    let mut env: BTreeMap<OsString, EnvEntry> = std::env::vars_os()
        .map(|(key, value)| {
            (
                EnvEntry::map_key(key.clone()),
                EnvEntry {
                    is_from_base_env: true,
                    preferred_key: key,
                    value,
                },
            )
        })
        .collect();

    #[cfg(unix)]
    {
        let key = EnvEntry::map_key("SHELL".into());
        // Only set the value of SHELL if it isn't already set
        if !env.contains_key(&key) {
            env.insert(
                EnvEntry::map_key("SHELL".into()),
                EnvEntry {
                    is_from_base_env: true,
                    preferred_key: "SHELL".into(),
                    value: get_shell().into(),
                },
            );
        }
    }

    #[cfg(windows)]
    {
        use std::os::windows::ffi::OsStringExt;
        use winapi::um::processenv::ExpandEnvironmentStringsW;
        use winreg::enums::{RegType, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE};
        use winreg::types::FromRegValue;
        use winreg::{RegKey, RegValue};

        fn reg_value_to_string(value: &RegValue) -> anyhow::Result<OsString> {
            match value.vtype {
                RegType::REG_EXPAND_SZ => {
                    let src = unsafe {
                        std::slice::from_raw_parts(
                            value.bytes.as_ptr() as *const u16,
                            value.bytes.len() / 2,
                        )
                    };
                    let size =
                        unsafe { ExpandEnvironmentStringsW(src.as_ptr(), std::ptr::null_mut(), 0) };
                    let mut buf = vec![0u16; size as usize + 1];
                    unsafe {
                        ExpandEnvironmentStringsW(src.as_ptr(), buf.as_mut_ptr(), buf.len() as u32)
                    };

                    let mut buf = buf.as_slice();
                    while let Some(0) = buf.last() {
                        buf = &buf[0..buf.len() - 1];
                    }
                    Ok(OsString::from_wide(buf))
                }
                _ => Ok(OsString::from_reg_value(value)?),
            }
        }

        if let Ok(sys_env) = RegKey::predef(HKEY_LOCAL_MACHINE)
```

--------------------------------

### Manage working directory

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Methods to set, clear, or retrieve the current working directory.

```rust
    pub fn cwd<D>(&mut self, dir: D)
    where
        D: AsRef<OsStr>,
    {
        self.cwd = Some(dir.as_ref().to_owned());
    }

    pub fn clear_cwd(&mut self) {
        self.cwd.take();
    }

    pub fn get_cwd(&self) -> Option<&OsString> {
        self.cwd.as_ref()
    }
```

--------------------------------

### Format as Unix command line

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Converts the configured command and arguments into a single string using Unix shell quoting conventions.

```rust
    /// Return the configured command and arguments as a single string,
    /// quoted per the unix shell conventions.
    pub fn as_unix_command_line(&self) -> anyhow::Result<String> {
        let mut strs = vec![];
        for arg in &self.args {
            let s = arg
                .to_str()
                .ok_or_else(|| anyhow::anyhow!("argument cannot be represented as utf8"))?;
            strs.push(s);
        }
        Ok(shell_words::join(strs))
    }
```

--------------------------------

### SerialTty::new

Source: https://docs.rs/portable-pty/latest/portable_pty/serial/struct.SerialTty.html

Creates a new instance of SerialTty for the specified port.

```APIDOC
## pub fn new<T: AsRef<OsStr> + ?Sized>(port: &T) -> Self

### Description
Creates a new SerialTty instance associated with the provided serial port path.

### Parameters
- **port** (&T) - Required - The path to the serial port device.
```

--------------------------------

### Open Pseudo-Terminal on Unix

Source: https://docs.rs/portable-pty/latest/src/portable_pty/unix.rs.html

Opens a master and slave pseudo-terminal pair using the libc openpty function.

```rust
fn openpty(size: PtySize) -> anyhow::Result<(UnixMasterPty, UnixSlavePty)> {
    let mut master: RawFd = -1;
    let mut slave: RawFd = -1;

    let mut size = winsize {
        ws_row: size.rows,
        ws_col: size.cols,
        ws_xpixel: size.pixel_width,
        ws_ypixel: size.pixel_height,
    };

    let result = unsafe {
        // BSDish systems may require mut pointers to some args
        #[allow(clippy::unnecessary_mut_passed)]
        libc::openpty(
            &mut master,
            &mut slave,
            ptr::null_mut(),
            ptr::null_mut(),
            &mut size,
        )
    };

    if result != 0 {
        bail!("failed to openpty: {:?}", io::Error::last_os_error());
    }

    let tty_name = tty_name(slave);

    let master = UnixMasterPty {
        fd: PtyFd(unsafe { FileDescriptor::from_raw_fd(master) }),
        took_writer: RefCell::new(false),
        tty_name,
    };
    let slave = UnixSlavePty {
        fd: PtyFd(unsafe { FileDescriptor::from_raw_fd(slave) }),
    };

    // Ensure that these descriptors will get closed when we execute
    // the child process.  This is done after constructing the Pty
    // instances so that we ensure that the Ptys get drop()'d if
    // the cloexec() functions fail (unlikely!).
    cloexec(master.fd.as_raw_fd())?;
    cloexec(slave.fd.as_raw_fd())?;

    Ok((master, slave))
}
```

--------------------------------

### SerialTty Configuration Methods

Source: https://docs.rs/portable-pty/latest/portable_pty/serial/struct.SerialTty.html

Methods to configure the serial port settings.

```APIDOC
## Configuration Methods

### set_baud_rate(baud: u32)
Sets the baud rate for the serial connection.

### set_char_size(char_size: CharSize)
Sets the character size for the serial connection.

### set_parity(parity: Parity)
Sets the parity for the serial connection.

### set_stop_bits(stop_bits: StopBits)
Sets the stop bits for the serial connection.

### set_flow_control(flow_control: FlowControl)
Sets the flow control for the serial connection.
```

--------------------------------

### Search Executable Path on Windows

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Locates an executable in the system PATH, optionally appending extensions defined in PATHEXT.

```rust
fn search_path(&self, exe: &OsStr) -> OsString {
        if let Some(path) = self.get_env("PATH") {
            let extensions = self.get_env("PATHEXT").unwrap_or(OsStr::new(".EXE"));
            for path in std::env::split_paths(&path) {
                // Check for exactly the user's string in this path dir
                let candidate = path.join(&exe);
                if candidate.exists() {
                    return candidate.into_os_string();
                }

                // otherwise try tacking on some extensions.
                // Note that this really replaces the extension in the
                // user specified path, so this is potentially wrong.
                for ext in std::env::split_paths(&extensions) {
                    // PATHEXT includes the leading `.`, but `with_extension`
                    // doesn't want that
                    let ext = ext.to_str().expect("PATHEXT entries must be utf8");
                    let path = path.join(&exe).with_extension(&ext[1..]);
                    if path.exists() {
                        return path.into_os_string();
                    }
                }
            }
        }

        exe.to_owned()
    }
```

--------------------------------

### Construct Windows Environment Block

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Encodes environment variables into a null-terminated wide character block suitable for CreateProcessW.

```rust
pub(crate) fn environment_block(&self) -> Vec<u16> {
        // encode the environment as wide characters
        let mut block = vec![];

        for EnvEntry {
            is_from_base_env: _,
            preferred_key,
            value,
        } in self.envs.values()
        {
            block.extend(preferred_key.encode_wide());
            block.push(b'=' as u16);
            block.extend(value.encode_wide());
            block.push(0);
        }
        // and a final terminator for CreateProcessW
        block.push(0);

        block
    }
```

--------------------------------

### Resize and Query PTY Window Size

Source: https://docs.rs/portable-pty/latest/src/portable_pty/unix.rs.html

Uses ioctl with TIOCSWINSZ and TIOCGWINSZ to set or retrieve the terminal window dimensions.

```rust
    fn resize(&self, size: PtySize) -> Result<(), Error> {
        let ws_size = winsize {
            ws_row: size.rows,
            ws_col: size.cols,
            ws_xpixel: size.pixel_width,
            ws_ypixel: size.pixel_height,
        };

        if unsafe {
            libc::ioctl(
                self.0.as_raw_fd(),
                libc::TIOCSWINSZ as _,
                &ws_size as *const _,
            )
        } != 0
        {
            bail!(
                "failed to ioctl(TIOCSWINSZ): {:?}",
                io::Error::last_os_error()
            );
        }

        Ok(())
    }
```

```rust
    fn get_size(&self) -> Result<PtySize, Error> {
        let mut size: winsize = unsafe { mem::zeroed() };
        if unsafe {
            libc::ioctl(
                self.0.as_raw_fd(),
                libc::TIOCGWINSZ as _,
                &mut size as *mut _,
            )
        } != 0
        {
            bail!(
                "failed to ioctl(TIOCGWINSZ): {:?}",
                io::Error::last_os_error()
            );
        }
        Ok(PtySize {
            rows: size.ws_row,
            cols: size.ws_col,
            pixel_width: size.ws_xpixel,
            pixel_height: size.ws_ypixel,
        })
    }
```

--------------------------------

### PtySystem::openpty

Source: https://docs.rs/portable-pty/latest/portable_pty

Opens a new pseudo-terminal pair with the specified dimensions.

```APIDOC
## PtySystem::openpty(size: PtySize)

### Description
Creates a new pseudo-terminal pair (master and slave) with the provided `PtySize` dimensions.

### Parameters
- **size** (PtySize) - The initial dimensions of the pty (rows, cols, pixel_width, pixel_height).
```

--------------------------------

### Initialize Native PTY System

Source: https://docs.rs/portable-pty/latest/src/portable_pty/lib.rs.html

Provides a factory function to retrieve the platform-specific PTY system implementation.

```rust
pub fn native_pty_system() -> Box<dyn PtySystem + Send> {
    Box::new(NativePtySystem::default())
}

#[cfg(unix)]
pub type NativePtySystem = unix::UnixPtySystem;
#[cfg(windows)]
pub type NativePtySystem = win::conpty::ConPtySystem;
```

--------------------------------

### Unix-specific configuration

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Unix-specific methods for setting umask and resolving executable paths.

```rust
#[cfg(unix)]
impl CommandBuilder {
    pub fn umask(&mut self, mask: Option<libc::mode_t>) {
        self.umask = mask;
    }

    fn resolve_path(&self) -> Option<&OsStr> {
        self.get_env("PATH")
    }

    fn search_path(&self, exe: &OsStr, cwd: &OsStr) -> anyhow::Result<OsString> {
        use nix::unistd::{access, AccessFlags};

        let exe_path: &Path = exe.as_ref();
        if exe_path.is_relative() {
            let cwd: &Path = cwd.as_ref();
            let mut errors = vec![];

            // If the requested executable is explicitly relative to cwd,
            // then check only there.
```

--------------------------------

### fn spawn_command

Source: https://docs.rs/portable-pty/latest/portable_pty/trait.SlavePty.html

Spawns a command into the pseudo-terminal using the provided CommandBuilder.

```APIDOC
### fn spawn_command(&self, cmd: CommandBuilder) -> Result<Box<dyn Child + Send + Sync>, Error>

#### Description
Spawns the command specified by the provided `CommandBuilder` into the pty.

#### Parameters
- **cmd** (CommandBuilder) - Required - The command configuration to be executed within the pty.

#### Returns
- **Result<Box<dyn Child + Send + Sync>, Error>** - Returns a handle to the spawned child process on success, or an Error if the command could not be spawned.
```

--------------------------------

### Manage environment variables

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Methods to set, remove, clear, or retrieve environment variables.

```rust
    /// Override the value of an environmental variable
    pub fn env<K, V>(&mut self, key: K, value: V)
    where
        K: AsRef<OsStr>,
        V: AsRef<OsStr>,
    {
        let key: OsString = key.as_ref().into();
        let value: OsString = value.as_ref().into();
        self.envs.insert(
            EnvEntry::map_key(key.clone()),
            EnvEntry {
                is_from_base_env: false,
                preferred_key: key,
                value: value,
            },
        );
    }

    pub fn env_remove<K>(&mut self, key: K)
    where
        K: AsRef<OsStr>,
    {
        let key = key.as_ref().into();
        self.envs.remove(&EnvEntry::map_key(key));
    }

    pub fn env_clear(&mut self) {
        self.envs.clear();
    }

    pub fn get_env<K>(&self, key: K) -> Option<&OsStr>
    where
        K: AsRef<OsStr>,
    {
        let key = key.as_ref().into();
        self.envs.get(&EnvEntry::map_key(key)).map(
            |EnvEntry {
                 is_from_base_env: _,
                 preferred_key: _,
                 value,
             }| value.as_os_str(),
        )
    }
```

--------------------------------

### Manage command arguments

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Methods for appending single or multiple arguments to the command line. Note that arg() will panic if the builder was created via new_default_prog.

```rust
    /// Append an argument to the current command line.
    /// Will panic if called on a builder created via `new_default_prog`.
    pub fn arg<S: AsRef<OsStr>>(&mut self, arg: S) {
        if self.is_default_prog() {
            panic!("attempted to add args to a default_prog builder");
        }
        self.args.push(arg.as_ref().to_owned());
    }

    /// Append a sequence of arguments to the current command line
    pub fn args<I, S>(&mut self, args: I)
    where
        I: IntoIterator<Item = S>,
        S: AsRef<OsStr>,
    {
        for arg in args {
            self.arg(arg);
        }
    }
```

--------------------------------

### CommandBuilder Environment Variable Tests

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Unit tests verifying environment variable setting, removal, clearing, and case-insensitive overrides on Windows.

```rust
#[cfg(test)]
mod tests {
    use super::*;

    #[cfg(unix)]
    #[test]
    fn test_cwd_relative() {
        assert!(is_cwd_relative_path("."));
        assert!(is_cwd_relative_path("./foo"));
        assert!(is_cwd_relative_path("../foo"));
        assert!(!is_cwd_relative_path("foo"));
        assert!(!is_cwd_relative_path("/foo"));
    }

    #[test]
    fn test_env() {
        let mut cmd = CommandBuilder::new("dummy");
        let package_authors = cmd.get_env("CARGO_PKG_AUTHORS");
        println!("package_authors: {:?}", package_authors);
        assert!(package_authors == Some(OsStr::new("Wez Furlong")));

        cmd.env("foo key", "foo value");
        cmd.env("bar key", "bar value");

        let iterated_envs = cmd.iter_extra_env_as_str().collect::<Vec<_>>();
        println!("iterated_envs: {:?}", iterated_envs);
        assert!(iterated_envs == vec![("bar key", "bar value"), ("foo key", "foo value")]);

        {
            let mut cmd = cmd.clone();
            cmd.env_remove("foo key");

            let iterated_envs = cmd.iter_extra_env_as_str().collect::<Vec<_>>();
            println!("iterated_envs: {:?}", iterated_envs);
            assert!(iterated_envs == vec![("bar key", "bar value")]);
        }

        {
            let mut cmd = cmd.clone();
            cmd.env_remove("bar key");

            let iterated_envs = cmd.iter_extra_env_as_str().collect::<Vec<_>>();
            println!("iterated_envs: {:?}", iterated_envs);
            assert!(iterated_envs == vec![("foo key", "foo value")]);
        }

        {
            let mut cmd = cmd.clone();
            cmd.env_clear();

            let iterated_envs = cmd.iter_extra_env_as_str().collect::<Vec<_>>();
            println!("iterated_envs: {:?}", iterated_envs);
            assert!(iterated_envs.is_empty());
        }
    }

    #[cfg(windows)]
    #[test]
    fn test_env_case_insensitive_override() {
        let mut cmd = CommandBuilder::new("dummy");
        cmd.env("Cargo_Pkg_Authors", "Not Wez");
        assert!(cmd.get_env("cargo_pkg_authors") == Some(OsStr::new("Not Wez")));

        cmd.env_remove("cARGO_pKG_aUTHORS");
        assert!(cmd.get_env("CARGO_PKG_AUTHORS").is_none());
    }
}
```

--------------------------------

### SlavePty::spawn_command

Source: https://docs.rs/portable-pty/latest/portable_pty

Spawns a command into the slave side of the pseudo-terminal.

```APIDOC
## SlavePty::spawn_command(cmd: CommandBuilder)

### Description
Spawns a process into the pty using the provided `CommandBuilder` configuration.

### Parameters
- **cmd** (CommandBuilder) - The command configuration to execute.
```

--------------------------------

### fn openpty(&self, size: PtySize) -> Result<PtyPair>

Source: https://docs.rs/portable-pty/latest/portable_pty/trait.PtySystem.html

Creates a new Pty instance with the specified dimensions, returning a master and slave Pty pair.

```APIDOC
### fn openpty(&self, size: PtySize) -> Result<PtyPair>

#### Description
Create a new Pty instance with the window size set to the specified dimensions. Returns a (master, slave) Pty pair. The master side is used to drive the slave side.

#### Parameters
- **size** (PtySize) - Required - The initial dimensions for the Pty instance.

#### Returns
- **Result<PtyPair>** - A Result containing the PtyPair on success, or an error if the operation fails.
```

--------------------------------

### Check if default program

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Returns true if the builder was initialized via new_default_prog.

```rust
    /// Returns true if this builder was created via `new_default_prog`
    pub fn is_default_prog(&self) -> bool {
        self.args.is_empty()
    }
```

--------------------------------

### Map environment keys for case-insensitive platforms

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Normalizes environment variable keys to lowercase on Windows to handle case-insensitivity.

```rust
fn map_key(k: OsString) -> OsString {
    if cfg!(windows) {
        // Best-effort lowercase transformation of an os string
        match k.to_str() {
            Some(s) => s.to_lowercase().into(),
            None => k,
        }
    } else {
        k
    }
}
```

--------------------------------

### resize

Source: https://docs.rs/portable-pty/latest/portable_pty/trait.MasterPty.html

Informs the kernel and the child process that the window has been resized, updating the winsize information and generating a signal.

```APIDOC
## fn resize(&self, size: PtySize) -> Result<(), Error>

### Description
Updates the kernel's winsize information for the pty and signals the child process to update its state accordingly.

### Parameters
- **size** (PtySize) - Required - The new dimensions for the pty.
```

--------------------------------

### UnixPtySystem Definition

Source: https://docs.rs/portable-pty/latest/portable_pty/unix/struct.UnixPtySystem.html

The structure definition for UnixPtySystem.

```rust
pub struct UnixPtySystem {}
```

--------------------------------

### Retrieve Shell Configuration

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Determines the shell to execute by checking the SHELL environment variable or falling back to system defaults.

```rust
    pub fn get_shell(&self) -> String {
        use nix::unistd::{access, AccessFlags};

        if let Some(shell) = self.get_env("SHELL").and_then(OsStr::to_str) {
```

--------------------------------

### PtySystem::openpty

Source: https://docs.rs/portable-pty/latest/portable_pty/serial/struct.SerialTty.html

Creates a new Pty instance with the specified dimensions.

```APIDOC
## fn openpty(&self, _size: PtySize) -> Result<PtyPair>

### Description
Creates a new Pty instance with the window size set to the specified dimensions. Returns a (master, slave) Pty pair where the master side is used to drive the slave side.

### Parameters
- **_size** (PtySize) - Required - The dimensions for the new Pty instance.
```

--------------------------------

### Convert to std::process::Command

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Converts the internal CommandBuilder state into a standard library Command, handling shell login prefixes and environment variables.

```rust
    pub(crate) fn as_command(&self) -> anyhow::Result<std::process::Command> {
        use std::os::unix::process::CommandExt;

        let home = self.get_home_dir()?;
        let dir: &OsStr = self
            .cwd
            .as_ref()
            .map(|dir| dir.as_os_str())
            .filter(|dir| std::path::Path::new(dir).is_dir())
            .unwrap_or(home.as_ref());
        let shell = self.get_shell();

        let mut cmd = if self.is_default_prog() {
            let mut cmd = std::process::Command::new(&shell);

            // Run the shell as a login shell by prefixing the shell's
            // basename with `-` and setting that as argv0
            let basename = shell.rsplit('/').next().unwrap_or(&shell);
            cmd.arg0(&format!("-", basename));
            cmd
        } else {
            let resolved = self.search_path(&self.args[0], dir)?;
            let mut cmd = std::process::Command::new(&resolved);
            cmd.arg0(&self.args[0]);
            cmd.args(&self.args[1..]);
            cmd
        };

        cmd.current_dir(dir);

        cmd.env_clear();
        cmd.env("SHELL", shell);
        cmd.envs(self.envs.values().map(
            |EnvEntry {
                 is_from_base_env: _,
                 preferred_key,
                 value,
             }| (preferred_key.as_os_str(), value.as_os_str()),
        ));

        Ok(cmd)
    }
```

--------------------------------

### ExitStatus Methods

Source: https://docs.rs/portable-pty/latest/portable_pty/struct.ExitStatus.html

Methods for constructing and querying the status of a child process.

```APIDOC
## pub fn with_exit_code(code: u32) -> Self

### Description
Constructs an ExitStatus from a process return code.

## pub fn with_signal(signal: &str) -> Self

### Description
Constructs an ExitStatus from a signal name.

## pub fn success(&self) -> bool

### Description
Returns true if the status indicates successful completion.

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

### Description
Returns the exit code that this ExitStatus was constructed with.

## pub fn signal(&self) -> Option<&str>

### Description
Returns the signal if present that this ExitStatus was constructed with.
```

--------------------------------

### Resolve Home Directory

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Attempts to resolve the user's home directory using environment variables or the system password database.

```rust
fn get_home_dir(&self) -> anyhow::Result<String> {
        if let Some(home_dir) = self.get_env("HOME").and_then(OsStr::to_str) {
            return Ok(home_dir.into());
        }

        let ent = unsafe { libc::getpwuid(libc::getuid()) };
        if ent.is_null() {
            Ok("/".into())
        } else {
            use std::ffi::CStr;
            use std::str;
            let home = unsafe { CStr::from_ptr((*ent).pw_dir) };
            home.to_str()
                .map(str::to_owned)
                .context("failed to resolve home dir")
        }
    }
```

--------------------------------

### Iterate environment variables

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Methods to iterate over extra or full environment variables as string slices.

```rust
    /// Iterate over the configured environment. Only includes environment
    /// variables set by the caller via `env`, not variables set in the base
    /// environment.
    pub fn iter_extra_env_as_str(&self) -> impl Iterator<Item = (&str, &str)> {
        self.envs.values().filter_map(
            |EnvEntry {
                 is_from_base_env,
                 preferred_key,
                 value,
             }| {
                if *is_from_base_env {
                    None
                } else {
                    let key = preferred_key.to_str()?;
                    let value = value.to_str()?;
                    Some((key, value))
                }
            },
        )
    }

    pub fn iter_full_env_as_str(&self) -> impl Iterator<Item = (&str, &str)> {
        self.envs.values().filter_map(
            |EnvEntry {
                 preferred_key,
                 value,
                 ..
             }| {
                let key = preferred_key.to_str()?;
                let value = value.to_str()?;
                Some((key, value))
            },
        )
    }
```

--------------------------------

### Registry Environment Variable Merging

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Logic for reading and merging system and user environment variables from the Windows registry.

```rust
            .open_subkey("System\\CurrentControlSet\\Control\\Session Manager\\Environment")
        {
            for res in sys_env.enum_values() {
                if let Ok((name, value)) = res {
                    if name.to_ascii_lowercase() == "username" {
                        continue;
                    }
                    if let Ok(value) = reg_value_to_string(&value) {
                        log::trace!("adding SYS env: {:?} {:?}", name, value);
                        env.insert(
                            EnvEntry::map_key(name.clone().into()),
                            EnvEntry {
                                is_from_base_env: true,
                                preferred_key: name.into(),
                                value,
                            },
                        );
                    }
                }
            }
        }

        if let Ok(sys_env) = RegKey::predef(HKEY_CURRENT_USER).open_subkey("Environment") {
            for res in sys_env.enum_values() {
                if let Ok((name, value)) = res {
                    if let Ok(value) = reg_value_to_string(&value) {
                        // Merge the system and user paths together
                        let value = if name.to_ascii_lowercase() == "path" {
                            match env.get(&EnvEntry::map_key(name.clone().into())) {
                                Some(entry) => {
                                    let mut result = OsString::new();
                                    result.push(&entry.value);
                                    result.push(";");
                                    result.push(&value);
                                    result
                                }
                                None => value,
                            }
                        } else {
                            value
                        };

                        log::trace!("adding USER env: {:?} {:?}", name, value);
                        env.insert(
                            EnvEntry::map_key(name.clone().into()),
                            EnvEntry {
                                is_from_base_env: true,
                                preferred_key: name.into(),
                                value,
                            },
                        );
                    }
                }
            }
        }
    }

    env
}
```

--------------------------------

### CommandBuilder Struct Definition

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

The core structure for managing command configuration, including arguments, environment, and terminal settings.

```rust
#[derive(Clone, Debug, PartialEq)]
#[cfg_attr(feature = "serde_support", derive(Serialize, Deserialize))]
pub struct CommandBuilder {
    args: Vec<OsString>,
    envs: BTreeMap<OsString, EnvEntry>,
    cwd: Option<OsString>,
    #[cfg(unix)]
    pub(crate) umask: Option<libc::mode_t>,
    controlling_tty: bool,
}
```

--------------------------------

### Spawn Process with PTY Configuration

Source: https://docs.rs/portable-pty/latest/src/portable_pty/unix.rs.html

Configures a child process to use the PTY as its controlling terminal, resets signal dispositions, and cleans up file descriptors.

```rust
    fn spawn_command(&self, builder: CommandBuilder) -> anyhow::Result<std::process::Child> {
        let configured_umask = builder.umask;

        let mut cmd = builder.as_command()?;
        let controlling_tty = builder.get_controlling_tty();

        unsafe {
            cmd.stdin(self.as_stdio()?)
                .stdout(self.as_stdio()?)
                .stderr(self.as_stdio()?)
                .pre_exec(move || {
                    // Clean up a few things before we exec the program
                    // Clear out any potentially problematic signal
                    // dispositions that we might have inherited
                    for signo in &[
                        libc::SIGCHLD,
                        libc::SIGHUP,
                        libc::SIGINT,
                        libc::SIGQUIT,
                        libc::SIGTERM,
                        libc::SIGALRM,
                    ] {
                        libc::signal(*signo, libc::SIG_DFL);
                    }

                    let empty_set: libc::sigset_t = std::mem::zeroed();
                    libc::sigprocmask(libc::SIG_SETMASK, &empty_set, std::ptr::null_mut());

                    // Establish ourselves as a session leader.
                    if libc::setsid() == -1 {
                        return Err(io::Error::last_os_error());
                    }

                    // Clippy wants us to explicitly cast TIOCSCTTY using
                    // type::from(), but the size and potentially signedness
                    // are system dependent, which is why we're using `as _`.
                    // Suppress this lint for this section of code.
                    #[allow(clippy::cast_lossless)]
                    if controlling_tty {
                        // Set the pty as the controlling terminal.
                        // Failure to do this means that delivery of
                        // SIGWINCH won't happen when we resize the
                        // terminal, among other undesirable effects.
                        if libc::ioctl(0, libc::TIOCSCTTY as _, 0) == -1 {
                            return Err(io::Error::last_os_error());
                        }
                    }

                    close_random_fds();

```

--------------------------------

### Resolve and Validate Executable Path

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Logic for checking if an executable exists, is a directory, or has appropriate execution permissions within the current working directory or system PATH.

```rust
            if is_cwd_relative_path(exe_path) {
                let abs_path = cwd.join(exe_path);

                if abs_path.is_dir() {
                    anyhow::bail!(
                        "Unable to spawn {} because it is a directory",
                        abs_path.display()
                    );
                } else if access(&abs_path, AccessFlags::X_OK).is_ok() {
                    return Ok(abs_path.into_os_string());
                } else if access(&abs_path, AccessFlags::F_OK).is_ok() {
                    anyhow::bail!(
                        "Unable to spawn {} because it is not executable",
                        abs_path.display()
                    );
                }

                anyhow::bail!(
                    "Unable to spawn {} because it does not exist",
                    abs_path.display()
                );
            }

            if let Some(path) = self.resolve_path() {
                for path in std::env::split_paths(&path) {
                    let candidate = cwd.join(&path).join(&exe);

                    if candidate.is_dir() {
                        errors.push(format!("{} exists but is a directory", candidate.display()));
                    } else if access(&candidate, AccessFlags::X_OK).is_ok() {
                        return Ok(candidate.into_os_string());
                    } else if access(&candidate, AccessFlags::F_OK).is_ok() {
                        errors.push(format!(
                            "{} exists but is not executable",
                            candidate.display()
                        ));
                    }
                }
                errors.push(format!("No viable candidates found in PATH {path:?}"));
            } else {
                errors.push("Unable to resolve the PATH".to_string());
            }
            anyhow::bail!(
                "Unable to spawn {} because:\n{}",
                exe_path.display(),
                errors.join(".\n")
            );
        } else if exe_path.is_dir() {
            anyhow::bail!(
                "Unable to spawn {} because it is a directory",
                exe_path.display()
            );
        } else {
            if let Err(err) = access(exe_path, AccessFlags::X_OK) {
                if access(exe_path, AccessFlags::F_OK).is_ok() {
                    anyhow::bail!(
                        "Unable to spawn {} because it is not executable ({err:#})",
                        exe_path.display()
                    );
                } else {
                    anyhow::bail!(
                        "Unable to spawn {} because it doesn't exist on the filesystem ({err:#})",
                        exe_path.display()
                    );
                }
            }

            Ok(exe.to_owned())
        }
    }
```

--------------------------------

### NativePtySystem Type Definition

Source: https://docs.rs/portable-pty/latest/portable_pty/type.NativePtySystem.html

The type alias definition for NativePtySystem.

```rust
pub type NativePtySystem = UnixPtySystem;
```

--------------------------------

### native_pty_system()

Source: https://docs.rs/portable-pty/latest/portable_pty/fn.native_pty_system.html

Returns a boxed instance of the platform-specific PtySystem trait implementation.

```APIDOC
## Function: native_pty_system

### Description
Returns a platform-specific implementation of the `PtySystem` trait. This function is used to initialize the PTY system for the current operating system.

### Signature
`pub fn native_pty_system() -> Box<dyn PtySystem + Send>`

### Returns
- **Box<dyn PtySystem + Send>** - A heap-allocated object implementing the `PtySystem` trait, safe to send across threads.
```

--------------------------------

### take_writer

Source: https://docs.rs/portable-pty/latest/portable_pty/trait.MasterPty.html

Obtains a writable handle to send data to the slave end of the pty.

```APIDOC
## fn take_writer(&self) -> Result<Box<dyn Write + Send>, Error>

### Description
Returns a boxed writer stream. Writing to this stream sends data to the slave. Dropping the writer sends an EOF to the slave. Note: It is invalid to call this method more than once.
```

--------------------------------

### Resolve default shell on Unix

Source: https://docs.rs/portable-pty/latest/src/portable_pty/cmdbuilder.rs.html

Retrieves the user's default shell from the passwd database, falling back to /bin/sh if unavailable or non-executable.

```rust
fn get_shell() -> String {
    use nix::unistd::{access, AccessFlags};
    use std::ffi::CStr;
    use std::str;

    let ent = unsafe { libc::getpwuid(libc::getuid()) };
    if !ent.is_null() {
        let shell = unsafe { CStr::from_ptr((*ent).pw_shell) };
        match shell.to_str().map(str::to_owned) {
            Err(err) => {
                log::warn!(
                    "passwd database shell could not be \
                     represented as utf-8: {err:#}, \
                     falling back to /bin/sh"
                );
            }
            Ok(shell) => {
                if let Err(err) = access(Path::new(&shell), AccessFlags::X_OK) {
                    log::warn!(
                        "passwd database shell={shell:?} which is \
                         not executable ({err:#}), falling back to /bin/sh"
                    );
                } else {
                    return shell;
                }
            }
        }
    }
    "/bin/sh".into()
}
```

--------------------------------

### Implement Child trait for std::process::Child

Source: https://docs.rs/portable-pty/latest/src/portable_pty/lib.rs.html

Provides a wrapper for standard process child management, including platform-specific handle access on Windows.

```rust
impl Child for std::process::Child {
    fn try_wait(&mut self) -> IoResult<Option<ExitStatus>> {
        std::process::Child::try_wait(self).map(|s| match s {
            Some(s) => Some(s.into()),
            None => None,
        })
    }

    fn wait(&mut self) -> IoResult<ExitStatus> {
        std::process::Child::wait(self).map(Into::into)
    }

    fn process_id(&self) -> Option<u32> {
        Some(self.id())
    }

    #[cfg(windows)]
    fn as_raw_handle(&self) -> Option<std::os::windows::io::RawHandle> {
        Some(std::os::windows::io::AsRawHandle::as_raw_handle(self))
    }
}
```

--------------------------------

### SerialTty Implementation

Source: https://docs.rs/portable-pty/latest/src/portable_pty/serial.rs.html

The core implementation of the SerialTty struct and its PtySystem trait, including configuration methods and the openpty logic.

```rust
//! This module implements a serial port based tty.
//! This is a bit different from the other implementations in that
//! we cannot explicitly spawn a process into the serial connection,
//! so we can only use a `CommandBuilder::new_default_prog` with the
//! `openpty` method.
//! On most (all?) systems, attempting to open multiple instances of
//! the same serial port will fail.
use crate::{
    Child, ChildKiller, CommandBuilder, ExitStatus, MasterPty, PtyPair, PtySize, PtySystem,
    SlavePty,
};
use anyhow::{ensure, Context};
use filedescriptor::FileDescriptor;
use serial2::{CharSize, FlowControl, Parity, SerialPort, StopBits};
use std::cell::RefCell;
use std::ffi::{OsStr, OsString};
use std::io::{Read, Result as IoResult, Write};
#[cfg(unix)]
use std::path::PathBuf;
use std::sync::Arc;
use std::time::Duration;

type Handle = Arc<SerialPort>;

pub struct SerialTty {
    port: OsString,
    baud: u32,
    char_size: CharSize,
    parity: Parity,
    stop_bits: StopBits,
    flow_control: FlowControl,
}

impl SerialTty {
    pub fn new<T: AsRef<OsStr> + ?Sized>(port: &T) -> Self {
        Self {
            port: port.as_ref().to_owned(),
            baud: 9600,
            char_size: CharSize::Bits8,
            parity: Parity::None,
            stop_bits: StopBits::One,
            flow_control: FlowControl::XonXoff,
        }
    }

    pub fn set_baud_rate(&mut self, baud: u32) {
        self.baud = baud;
    }

    pub fn set_char_size(&mut self, char_size: CharSize) {
        self.char_size = char_size;
    }

    pub fn set_parity(&mut self, parity: Parity) {
        self.parity = parity;
    }

    pub fn set_stop_bits(&mut self, stop_bits: StopBits) {
        self.stop_bits = stop_bits;
    }

    pub fn set_flow_control(&mut self, flow_control: FlowControl) {
        self.flow_control = flow_control;
    }
}

impl PtySystem for SerialTty {
    fn openpty(&self, _size: PtySize) -> anyhow::Result<PtyPair> {
        let mut port = SerialPort::open(&self.port, self.baud)
            .with_context(|| format!("openpty on serial port {:?}", self.port))?;

        let mut settings = port.get_configuration()?;
        settings.set_raw();
        settings.set_baud_rate(self.baud)?;
        settings.set_char_size(self.char_size);
        settings.set_flow_control(self.flow_control);
        settings.set_parity(self.parity);
        settings.set_stop_bits(self.stop_bits);
        log::debug!("serial settings: {:#?}", port.get_configuration());
        port.set_configuration(&settings)?;

        // The timeout needs to be rather short because, at least on Windows,
        // a read with a long timeout will block a concurrent write from
        // happening.  In wezterm we tend to have a thread looping on read
        // while writes happen occasionally from the gui thread, and if we
        // make this timeout too long we can block the gui thread.
        port.set_read_timeout(Duration::from_millis(50))?;
        port.set_write_timeout(Duration::from_millis(50))?;

        let port: Handle = Arc::new(port);

        Ok(PtyPair {
            slave: Box::new(Slave {
                port: Arc::clone(&port),
            }),
            master: Box::new(Master {
                port,
                took_writer: RefCell::new(false),
            }),
        })
    }
}

struct Slave {
    port: Handle,
}

impl SlavePty for Slave {
    fn spawn_command(&self, cmd: CommandBuilder) -> anyhow::Result<Box<dyn Child + Send + Sync>> {
        ensure!(
            cmd.is_default_prog(),
            "can only use default prog commands with serial tty implementations"
        );
        Ok(Box::new(SerialChild {
            port: Arc::clone(&self.port),
        }))
    }
}

/// There isn't really a child process on the end of the serial connection,
/// so all of the Child trait impls are NOP
struct SerialChild {
    port: Handle,
}

// An anemic impl of Debug to satisfy some indirect trait bounds
impl std::fmt::Debug for SerialChild {
    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
        fmt.debug_struct("SerialChild").finish()
    }
}

impl Child for SerialChild {
    fn try_wait(&mut self) -> IoResult<Option<ExitStatus>> {
        Ok(None)
    }

    fn wait(&mut self) -> IoResult<ExitStatus> {
        // There isn't really a child process to wait for,
        // as the serial connection never really "dies",
        // however, for something like a USB serial port,

```