std.process

std.process exposes checked process-argument helpers and an explicit exit primitive.

Arguments

export def process_arg_count() -> usize

export enum ProcessArgError:
    case OutOfRange
    case InvalidUtf8

export def process_arg(index: usize) -> Result[String, ProcessArgError]
export def process_arg_path(index: usize) -> Result[PathBuf, ProcessArgError]

• process_arg_count() is the count of program-level arguments (not counting argv[0]).
• process_arg(0) returns the first user argument as an owned String.
• process_arg_path(0) returns it as an owned PathBuf, appropriate when the argument is a filesystem path and may legally contain non-UTF-8 bytes.

ProcessArgError::OutOfRange is returned when index >= process_arg_count(). ProcessArgError::InvalidUtf8 is returned from process_arg when the underlying bytes are not valid UTF-8; process_arg_path is byte-shaped and does not surface this error.

Exit

export def process_exit(code: i32) -> None

Equivalent to libc exit(code). Use this for early exits from a program whose main returns None; for programs whose main returns i32, just return the code.

Example

import std.io as io
import std.process as process

def main() -> i32:
    let arg_result: Result[String, ProcessArgError] = process.process_arg(0)
    match arg_result:
        case Ok(name):
            io.stdout_write_str("hello, ")
            io.stdout_write_str(name.as_str())
            io.stdout_write_str("\n")
            return 0
        case Err:
            io.stderr_write_str("usage: greet NAME\n")
            return 1