kopt

kopt is a small command line parser library for the JVM.

kopt is fully compatible with Java 8 and Kotlin 1.1 (or later).

Specification

1. Command line
   

   1. Terminating option parsing
      A double hyphen delimiter followed by a whitespace character (e.g. -- ) terminates option parsing. Thus, section (3) is effectively irrelevant for anything that is parsed after this character sequence and even literals prefixed with hyphens are interpreted as arguments.

2. Arguments
   Arguments are interpreted index-based.

   1. Optional arguments
      An argument may be optional, that is, it is not required to pass a value for said argument.

      1. An optional argument must only be followed by other optional arguments.

   2. Vararg arguments
      The trailing argument may be a vararg argument, that is,

      1. A vararg argument must always be the trailing argument.
      2. A vararg argument may be optional.

3. Options
   Options are interpreted key-based.

   1. Option tokens An option token is used to identify an option. Two different kinds of tokens exist.

      • Option tokens are case-sensitive.

      1. Long token
         A long token is an alphanumeric literal.

         An alphanumeric literal prefixed with a double hyphen delimiter (--) is interpreted as long option token.

      2. Short token
         A short token is an alphabetic character.

         An alphabetic character prefixed with a single hyphen delimiter (-) is interpreted as short option token.

         Multiple short tokens may be chained behind a single hyphen delimiter. Thus, -a -b -c and -abc are equivalent. (Furthermore, -a <value> -b <value> -c <value> and -abc <value> are equivalent.) Short tokens may only be chained if the way the represented options parse values do not conflict.

         • Default options and marker options must be followed by a value.
         • Marker options and marker-only options may not be followed by a value.
         • Default options and marker-only options may not be chained.

         An alphabetic literal prefixed with a single hyphen delimiter (-) is interpreted as a set of chained short option tokens.

      If an option token and a following string are separated by either an equals sign (=) or a single whitespace character (e.g. a space ), the string is interpreted as a value for the option represented by the token.

   2. Marker options
      An option may be a marker option, that is, the option does not require a value to be passed and will instead use a predefined value if the option is present and no value is passed.
      Additionally, an option may be a marker-only option, that is, the option does not accept a value to be passed.

Grammar

Notation

This section informally explains the grammar notation used below.

Symbols and naming

• Terminal symbol names start with an uppercase letter, e.g. String.
• Nonterminal symbol names start with lowercase letter, e.g. commandLine.
• Each production starts with a colon (:).
• Symbol definitions may have many productions and are terminated by a semicolon (;).
• Symbol definitions may be prepended with attributes, e.g. start attribute denotes a start symbol.

EBNF expressions

• Operator | denotes alternative.
• Operator * denotes iteration (zero or more).
• Operator + denotes iteration (one or more).
• Operator ? denotes option (zero or one).

Syntax

start
commandLine
   : argument+ ("--" string*)?
   ;

argument
   : String
   : option
   ;
   
option
   : defaultOption
   : markerOption
   : markerOnlyOption
   ;
   
defaultOption
   : "-" ShortToken+ "=" String
   : "-" ShortToken+ " " String
   : "--" LongToken "=" String
   : "--" LongToken " " String
   ;
   
markerOption
   : defaultOption
   : markerOnlyOption
   ;

markerOnlyOption
   : "-" ShortToken+
   : "--" LongToken
   ;

ShortOptionToken
   : <any alphabetic character>
   ;
   
LongOptionToken
   : <any alphanumeric character>+
   ;

String
   : <any non-whitespace character>+
   : "\"" <any character>* "\""
   ;