#parser #env #lang #parse


Parser für Kommandozeilen-Argumente mit optionaler, automatischer Hilfe-Generierung

6 releases

0.2.1 Jul 4, 2022
0.2.0 Mar 28, 2022
0.1.3 Mar 2, 2022
0.1.1 Feb 3, 2022
0.1.0 Jan 18, 2022

#238 in Command-line interface

MIT license



Anmerkung: Dies ist die englische ReadMe, für die deutsche Version siehe LIESMICH.md.

TODO english version

Parser for command line arguments with optional automatic help generation.

Arguments are created with the provided associated functions, the result type is specified with a type variable. Arguments can be combined to more complex structures using more than one argument with the combine! macro, or one of the dedicated combineN functions.

Arguments are identified by their long names and potentially their short names. Long names are usually given after two minus characters --long. Short names are usually given after one minus character -short. Short names are expected to consist of only one Grapheme.

All Strings can be adjusted, e.g. description of an argument in the help message. Specialized functions for a german and english version are available if it is relevant. Additionally, german an english synonyms are available. Avoiding repetition of strings can be achieved using the Language type.

An Argument can have a default value, which is used if none of its names are used. Without a default value the argument must be used, resulting in a parse error otherwise.


Arguments without values are called flags, they can be active or inactive. In most cases they represent bool arguments, but other types are also supported.

A flag with long name flag, long_prefix --, short name f, short_prefix -, invert_prefix no and invert_prefix - can be activated with --flag or -f and deactivated with --no-flag.

If several flags with short names f, g and h exist they can be activated together with -fgh.

Early Exit

A special kind of flag argument causing an early exit. They can't be deactivated and cause an early exit with an associated message. Typical use cases are displaying of the current version or the help text.


Arguments can specify values. When specified with a long name, the value can be given after a space or the = character. Using a short name it is possible to specify it directly after the name. The value is parsed from a OsString.

It is possible to show all allowed values in the generated help text.

A value argument with long name value, long_prefix --, short name v, short_prefix - and value_infix = for a number type is parsed with result 3 for each of the following inputs:

  • --value 3
  • --value=3
  • -v 3
  • -v=3
  • -v3

Feature "derive"

Accepted command line arguments can be produced automatically using the derive feature. It allows deriving an implementation of the Parse trait for a struct with named fields.

The long name of the argument is the field name, the description in the help text is the docstring of the field.

The argument is parsed according to the ParseArgument trait. Instances exist for bool, String, number types (i8, u8, i16, u16, ..., f32, f64), Option<T> and instances of the EnumArgument trait. bool fields produce flag arguments which are off by default. Every other (provided) type produces a value argument; Option<T> has default value None, all other types produce required arguments. It is possible to derive an implementation of the EnumArgument trait for enum types holding no data. Types used as a ParseArgument must be an instance of Display.

The default behaviour can be changed using #[kommandozeilen_argumente(<Optionen>)] attributes.

The following options are supported at the struct declaration.

  • sprache: <sprache> | language: <language>: Default value for some strings, default: english. Builtin languages for deutsch, englisch and english.
  • version: create a --version, -v flag.
  • hilfe | help: create a help text flag.
  • hilfe(<opts>), help(<opts>), version(<opts>): Similar to the variant without ops, but short name is off by default. Possible Opts:
    • lang_präfix: <präfix> | long_prefix: <prefix>: Prefix before long name.
    • lang: <name>, long [<namen>]: Overwrite long name.
    • kurz_präfix: <präfix> | short_prefix: <prefix>: Prefix before short name.
    • kurz: Set short name as first Grapheme of the first long name.
    • kurz: <name>, kurz: [<namen>]: Overwrite short name.
    • sprache: <sprache> | language: <language>: Language of the help text and default names.
    • beschreibung: <programm-beschreibung> | description: <program_description>: Only supported for hilfe(<opts>) and help(<opts>). Set the program description shown in the help text.
  • case: sensitive, case: insensitive: All Strings (Names, prefix, infix) are parse case-sensitive or -insensitive, default: case: sensitive.
  • case(<opts>): Specific control about case-sensitivity. All opts have the form <name>: <value>, <value> must be one of sensitive and insensitive. Allowed Names:
    • lang_präfix | long_prefix
    • lang | long
    • kurz_präfix | short_prefix
    • kurz | short
    • invertiere_präfix | invert_prefix
    • invertiere_infix | invert_infix
    • wert_infix | value_infix
  • lang_präfix: <präfix> | long_prefix: <prefix>: Overwrite default value for prefix before long names, default: --.
  • kurz_präfix: <präfix> | short_prefix: <prefix>: Overwrite default value for prefix before short names, default: -.
  • invertiere_präfix: <string> | invert_prefix: <string>: Overwrite default value for prefix to invert a flag, default: kein or no.
  • invertiere_infix: <string> | invert_infix: <string>: Overwrite default value for infix after prefix to invert a flag, default -.
  • wert_infix: <string> | value_infix: <string>: Overwrite default value for infix to give a value in the same argument, default =.
  • meta_var: <string> | meta_var: <string>: Overwrite default value for the meta variable shown in the help text, default: WERT or VALUE.

Field support the following options:

  • glätten/flatten: Use the Parse trait (include the configured arguments).
  • FromStr: Use the FromStr trait (Display instance required for both value and error type).
  • benötigt/required: Don't use the configured default value.
  • lang_präfix: <präfix> | long_prefix: <prefix>: Prefix before long name.
  • lang: <name> | long: <name>: Overwrite long name.
  • lang: [<namen>] | long: [<names>]: Set multiple long names (comma separated list).
  • kurz_präfix: <präfix> | short_prefix: <prefix>: Prefix before short name.
  • kurz/short: Set short name as first Grapheme of the first long name.
  • kurz: <wert>"/short: <value>": Overwrite the short name.
  • kurz: [<namen>] | short: [<names>]: Set multiple short names (comma separated list).
  • standard: <wert> | default: <value>: Overwrite default value.
  • invertiere_präfix: <string> | invert_prefix: <string>: Overwrite prefix to invert a flag.
  • invertiere_infix: <string> | invert_infix: <string>: Overwrite infix after prefix to invert a flag.
  • wert_infix: <string> | value_infix: <string>: Overwrite infix to give the value in the same argument.
  • meta_var: <string>: Overwrite meta variable used in the help text.


A simple example for a struct with 3 flags and 2 value, created using the function API and the derive API are available in the GitHub repository. Both cases produce the following help text:

kommandozeilen_argumente 0.2.0
program description.

derive_en.exe [OPTIONS]

  --[no]-flag                         A flag with default settings. [Default: false]
  --[no]-(other|names)  | -u          A flag with alternative names. [Default: false]
  --[kein]-required     | -r          A flag without default value, with alternative prefix to invert the flag.
  --value(=| )VALUE                   A String value.
  --enumeration(=| )VAR | -e[=| ]VAR  An Enumeration-value with default value and alternative meta variable. [Possible values: One, Two, Three | Default: Two]
  --version             | -v          Show the current version.
  --help                | -h          Show this text.

Missing (planned) Features

  • subcommands
  • position-based arguments
  • Different default value for name without value and name doesn't appear
  • argument-groups (only one of these N flags can be active)


~64K SLoC