Custom parser for argument values

Pre-existing TypedValueParser implementations include:

• Fn(&str) -> Result<T, E>
• EnumValueParser and PossibleValuesParser for static enumerated values
• BoolishValueParser and FalseyValueParser for alternative bool implementations
• RangedI64ValueParser and RangedU64ValueParser
• NonEmptyStringValueParser

Example

# use clap_builder as clap;
type EnvVar = (String, Option<String>);
fn parse_env_var(env: &str) -> Result<EnvVar, std::io::Error> {
    if let Some((var, value)) = env.split_once('=') {
        Ok((var.to_owned(), Some(value.to_owned())))
    } else {
        Ok((env.to_owned(), None))
    }
}

let mut cmd = clap::Command::new("raw")
    .arg(
        clap::Arg::new("env")
            .value_parser(clap::builder::ValueParser::new(parse_env_var))
            .required(true)
    );

let m = cmd.try_get_matches_from_mut(["cmd", "key=value"]).unwrap();
let port: &EnvVar = m.get_one("env")
    .expect("required");
assert_eq!(*port, ("key".into(), Some("value".into())));

bool parser for argument values

See also:

• BoolishValueParser for different human readable bool representations
• FalseyValueParser for assuming non-false is true

Example

# use clap_builder as clap;
let mut cmd = clap::Command::new("raw")
    .arg(
        clap::Arg::new("download")
            .value_parser(clap::value_parser!(bool))
            .required(true)
    );

let m = cmd.try_get_matches_from_mut(["cmd", "true"]).unwrap();
let port: bool = *m.get_one("download")
    .expect("required");
assert_eq!(port, true);

assert!(cmd.try_get_matches_from_mut(["cmd", "forever"]).is_err());

String parser for argument values

See also:

• NonEmptyStringValueParser

Example

# use clap_builder as clap;
let mut cmd = clap::Command::new("raw")
    .arg(
        clap::Arg::new("port")
            .value_parser(clap::value_parser!(String))
            .required(true)
    );

let m = cmd.try_get_matches_from_mut(["cmd", "80"]).unwrap();
let port: &String = m.get_one("port")
    .expect("required");
assert_eq!(port, "80");

[OsString][std::ffi::OsString] parser for argument values

Example

# #[cfg(unix)] {
# use clap_builder as clap;
# use clap::{Command, Arg, builder::ValueParser};
use std::ffi::OsString;
use std::os::unix::ffi::{OsStrExt,OsStringExt};
let r = Command::new("myprog")
    .arg(
        Arg::new("arg")
        .required(true)
        .value_parser(ValueParser::os_string())
    )
    .try_get_matches_from(vec![
        OsString::from("myprog"),
        OsString::from_vec(vec![0xe9])
    ]);

assert!(r.is_ok());
let m = r.unwrap();
let arg: &OsString = m.get_one("arg")
    .expect("required");
assert_eq!(arg.as_bytes(), &[0xe9]);
# }

[PathBuf][std::path::PathBuf] parser for argument values

Example

# use clap_builder as clap;
# use std::path::PathBuf;
# use std::path::Path;
let mut cmd = clap::Command::new("raw")
    .arg(
        clap::Arg::new("output")
            .value_parser(clap::value_parser!(PathBuf))
            .required(true)
    );

let m = cmd.try_get_matches_from_mut(["cmd", "hello.txt"]).unwrap();
let port: &PathBuf = m.get_one("output")
    .expect("required");
assert_eq!(port, Path::new("hello.txt"));

assert!(cmd.try_get_matches_from_mut(["cmd", ""]).is_err());

Describes the content of AnyValue

Reflect on enumerated value properties

Error checking should not be done with this; it is mostly targeted at user-facing applications like errors and completion.