Enum ErrorKind

pub enum ErrorKind {
    InvalidValue,
    UnknownArgument,
    InvalidSubcommand,
    UnrecognizedSubcommand,
    EmptyValue,
    ValueValidation,
    TooManyValues,
    TooFewValues,
    WrongNumberOfValues,
    ArgumentConflict,
    MissingRequiredArgument,
    MissingSubcommand,
    MissingArgumentOrSubcommand,
    UnexpectedMultipleUsage,
    InvalidUtf8,
    HelpDisplayed,
    VersionDisplayed,
    ArgumentNotFound,
    Io,
    Format,
}

Command line argument parser kind of error

Variants

InvalidValue

Occurs when an Arg has a set of possible values, and the user provides a value which isn’t in that set.

Examples

let result = App::new("prog")
    .arg(Arg::with_name("speed")
        .possible_value("fast")
        .possible_value("slow"))
    .get_matches_from_safe(vec!["prog", "other"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::InvalidValue);

UnknownArgument

Occurs when a user provides a flag, option, argument or subcommand which isn’t defined.

Examples

let result = App::new("prog")
    .arg(Arg::from_usage("--flag 'some flag'"))
    .get_matches_from_safe(vec!["prog", "--other"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::UnknownArgument);

InvalidSubcommand

Occurs when the user provides an unrecognized SubCommand which meets the threshold for being similar enough to an existing subcommand. If it doesn’t meet the threshold, or the ‘suggestions’ feature is disabled, the more general UnknownArgument error is returned.

Examples

let result = App::new("prog")
   .subcommand(SubCommand::with_name("config")
       .about("Used for configuration")
       .arg(Arg::with_name("config_file")
           .help("The configuration file to use")
           .index(1)))
   .get_matches_from_safe(vec!["prog", "confi"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::InvalidSubcommand);

UnrecognizedSubcommand

Occurs when the user provides an unrecognized SubCommand which either doesn’t meet the threshold for being similar enough to an existing subcommand, or the ‘suggestions’ feature is disabled. Otherwise the more detailed InvalidSubcommand error is returned.

This error typically happens when passing additional subcommand names to the help subcommand. Otherwise, the more general UnknownArgument error is used.

Examples

let result = App::new("prog")
    .subcommand(SubCommand::with_name("config")
        .about("Used for configuration")
        .arg(Arg::with_name("config_file")
            .help("The configuration file to use")
            .index(1)))
    .get_matches_from_safe(vec!["prog", "help", "nothing"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::UnrecognizedSubcommand);

EmptyValue

Occurs when the user provides an empty value for an option that does not allow empty values.

Examples

let res = App::new("prog")
    .arg(Arg::with_name("color")
         .long("color")
         .empty_values(false))
    .get_matches_from_safe(vec!["prog", "--color="]);
assert!(res.is_err());
assert_eq!(res.unwrap_err().kind, ErrorKind::EmptyValue);

ValueValidation

Occurs when the user provides a value for an argument with a custom validation and the value fails that validation.

Examples

fn is_numeric(val: String) -> Result<(), String> {
    match val.parse::<i64>() {
        Ok(..) => Ok(()),
        Err(..) => Err(String::from("Value wasn't a number!")),
    }
}

let result = App::new("prog")
    .arg(Arg::with_name("num")
         .validator(is_numeric))
    .get_matches_from_safe(vec!["prog", "NotANumber"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::ValueValidation);

TooManyValues

Occurs when a user provides more values for an argument than were defined by setting Arg::max_values.

Examples

let result = App::new("prog")
    .arg(Arg::with_name("arg")
        .multiple(true)
        .max_values(2))
    .get_matches_from_safe(vec!["prog", "too", "many", "values"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::TooManyValues);

TooFewValues

Occurs when the user provides fewer values for an argument than were defined by setting Arg::min_values.

Examples

let result = App::new("prog")
    .arg(Arg::with_name("some_opt")
        .long("opt")
        .min_values(3))
    .get_matches_from_safe(vec!["prog", "--opt", "too", "few"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::TooFewValues);

WrongNumberOfValues

Occurs when the user provides a different number of values for an argument than what’s been defined by setting Arg::number_of_values or than was implicitly set by Arg::value_names.

Examples

let result = App::new("prog")
    .arg(Arg::with_name("some_opt")
        .long("opt")
        .takes_value(true)
        .number_of_values(2))
    .get_matches_from_safe(vec!["prog", "--opt", "wrong"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::WrongNumberOfValues);

ArgumentConflict

Occurs when the user provides two values which conflict with each other and can’t be used together.

Examples

let result = App::new("prog")
    .arg(Arg::with_name("debug")
        .long("debug")
        .conflicts_with("color"))
    .arg(Arg::with_name("color")
        .long("color"))
    .get_matches_from_safe(vec!["prog", "--debug", "--color"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::ArgumentConflict);

MissingRequiredArgument

Occurs when the user does not provide one or more required arguments.

Examples

let result = App::new("prog")
    .arg(Arg::with_name("debug")
        .required(true))
    .get_matches_from_safe(vec!["prog"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::MissingRequiredArgument);

MissingSubcommand

Occurs when a subcommand is required (as defined by AppSettings::SubcommandRequired), but the user does not provide one.

Examples

let err = App::new("prog")
    .setting(AppSettings::SubcommandRequired)
    .subcommand(SubCommand::with_name("test"))
    .get_matches_from_safe(vec![
        "myprog",
    ]);
assert!(err.is_err());
assert_eq!(err.unwrap_err().kind, ErrorKind::MissingSubcommand);

MissingArgumentOrSubcommand

Occurs when either an argument or SubCommand is required, as defined by AppSettings::ArgRequiredElseHelp, but the user did not provide one.

Examples

let result = App::new("prog")
    .setting(AppSettings::ArgRequiredElseHelp)
    .subcommand(SubCommand::with_name("config")
        .about("Used for configuration")
        .arg(Arg::with_name("config_file")
            .help("The configuration file to use")))
    .get_matches_from_safe(vec!["prog"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::MissingArgumentOrSubcommand);

UnexpectedMultipleUsage

Occurs when the user provides multiple values to an argument which doesn’t allow that.

Examples

let result = App::new("prog")
    .arg(Arg::with_name("debug")
        .long("debug")
        .multiple(false))
    .get_matches_from_safe(vec!["prog", "--debug", "--debug"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::UnexpectedMultipleUsage);

InvalidUtf8

Occurs when the user provides a value containing invalid UTF-8 for an argument and AppSettings::StrictUtf8 is set.

Platform Specific

Non-Windows platforms only (such as Linux, Unix, macOS, etc.)

Examples

let result = App::new("prog")
   .setting(AppSettings::StrictUtf8)
   .arg(Arg::with_name("utf8")
       .short("u")
       .takes_value(true))
   .get_matches_from_safe(vec![OsString::from("myprog"),
                               OsString::from("-u"),
                               OsString::from_vec(vec![0xE9])]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::InvalidUtf8);

HelpDisplayed

Not a true “error” as it means --help or similar was used. The help message will be sent to stdout.

Note: If the help is displayed due to an error (such as missing subcommands) it will be sent to stderr instead of stdout.

Examples

let result = App::new("prog")
    .get_matches_from_safe(vec!["prog", "--help"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::HelpDisplayed);

VersionDisplayed

Not a true “error” as it means --version or similar was used. The message will be sent to stdout.

Examples

let result = App::new("prog")
    .get_matches_from_safe(vec!["prog", "--version"]);
assert!(result.is_err());
assert_eq!(result.unwrap_err().kind, ErrorKind::VersionDisplayed);

ArgumentNotFound

Occurs when using the value_t! and values_t! macros to convert an argument value into type T, but the argument you requested wasn’t used. I.e. you asked for an argument with name config to be converted, but config wasn’t used by the user. value_t!: ./macro.value_t!.html values_t!: ./macro.values_t!.html

Io

Represents an [I/O error]. Can occur when writing to stderr or stdout or reading a configuration file. [I/O error]: https://doc.rust-lang.org/std/io/struct.Error.html

Format

Represents a Format error (which is a part of Display). Typically caused by writing to stderr or stdout.

Trait Implementations

impl Clone for ErrorKind

fn clone(&self) -> ErrorKind

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ErrorKind

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl PartialEq for ErrorKind

fn eq(&self, other: &ErrorKind) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for ErrorKind

impl StructuralPartialEq for ErrorKind