[][src]Crate simpleargs

Simple argument parser

The goals of this library are to correctly handle OsString and produce high-quality error messages.

This library is like the traditional getopt with better error reporting. It converts an iterator of String or OsString to positional arguments and named arguments.

Single and double hyphens are considered equivalent. This means that -help and --help are equivalent. Opinion: Most new projects should parse each argument as a separate flag. So, -abc should be parsed as one argument named "abc", not three arguments named "a", "b", and "c". Combining multiple flags into one argument is confusing, so it should only be used for programs that are called interactively very frequently, like ls.

Options which take values can take values either as one argument, -option=value, or as two arguments, -option value.


use simpleargs::{Arg, Args, UsageError, OptionError};
use std::ffi::OsString;
use std::str::FromStr;

fn parse_args<T>(mut args: Args<T>) -> Result<(), UsageError<OsString>>
    T: Iterator<Item = OsString>,
    // The input file
    let mut input: Option<OsString> = None;
    // True if -flag was set
    let mut flag = false;
    // The value of -xvalue, if it was used
    let mut xvalue: Option<i32> = None;
    loop {
        match args.next() {
            Arg::Positional(arg) => if input.is_some() {
                return Err(UsageError::UnexpectedArgument { arg });
            } else {
                input = Some(arg)
            Arg::Named(arg) => arg.parse(|name, value| match name {
                "flag" => {
                    // parse() above will return an error for -flag=value,
                    // because this function does not use 'value'.
                    flag = true;
                "xvalue" => {
                    // Call as_str() for a str, or as_osstr() for OsStr.
                    xvalue = Some(i32::from_str(value.as_str()?)?);
                _ => Err(OptionError::Unknown),
            Arg::End => break,
            Arg::Error(err) => return Err(err),
    let input = match input {
        Some(path) => path,
        None => return Err(UsageError::MissingArgument { name: "input".to_owned() }),



Low-level argument parsing.



A stream of arguments.


A named command-line argument which may or may not have an associated value.


A handle for getting the value associated with a named flag.UsageError



A single argument in a stream of arguments.


An error for an invalid named argument.


A command-line usage error, for when the user has passed incorrect arguments to the program.