CommandLine.Option (picocli 3.6.0 API)

@Retention(value=RUNTIME)
 @Target(value={FIELD,METHOD,PARAMETER})
public static @interface CommandLine.Option

Annotate fields in your class with @Option and picocli will initialize these fields when matching arguments are specified on the command line. In the case of command methods (annotated with @Command), command options can be defined by annotating method parameters with @Option.

Command class example:

 import static picocli.CommandLine.*;

 public class MyClass {
     @Parameters(description = "Any number of input files")
     private List<File> files = new ArrayList<File>();

     @Option(names = { "-o", "--out" }, description = "Output file (default: print to console)")
     private File outputFile;

     @Option(names = { "-v", "--verbose"}, description = "Verbose mode. Helpful for troubleshooting. Multiple -v options increase the verbosity.")
     private boolean[] verbose;

     @Option(names = { "-h", "--help", "-?", "-help"}, usageHelp = true, description = "Display this help and exit")
     private boolean help;
 }

A field cannot be annotated with both @Parameters and @Option or a ParameterException is thrown.

Required Element Summary

Required Elements
Modifier and Type Required Element and Description

java.lang.String[] names
One or more option names.

Required Elements
Modifier and Type	Required Element and Description
`java.lang.String[]`	`names` One or more option names.

Optional Element Summary

Optional Elements
Modifier and Type	Optional Element and Description
`java.lang.String`	`arity` Specifies the minimum number of required parameters and the maximum number of accepted parameters.
`java.lang.Class<? extends java.lang.Iterable<java.lang.String>>`	`completionCandidates` Use this attribute to specify an `Iterable<String>` class that generates completion candidates for this option.
`java.lang.Class<? extends CommandLine.ITypeConverter<?>>[]`	`converter` Optionally specify one or more `CommandLine.ITypeConverter` classes to use to convert the command line argument into a strongly typed value (or key-value pair for map fields).
`java.lang.String`	`defaultValue` Returns the default value of this option, before splitting and type conversion.
`java.lang.String[]`	`description` Description of this option, used when generating the usage documentation.
`java.lang.String`	`descriptionKey` ResourceBundle key for this option.
`boolean`	`help` Deprecated. Use `usageHelp()` and `versionHelp()` instead. See `CommandLine.printHelpIfRequested(List, PrintStream, CommandLine.Help.Ansi)`
`boolean`	`hidden` Set `hidden=true` if this option should not be included in the usage help message.
`boolean`	`hideParamSyntax` Returns whether usage syntax decorations around the paramLabel should be suppressed.
`boolean`	`interactive` Set `interactive=true` if this option will prompt the end user for a value (like a password).
`java.lang.String`	`paramLabel` Specify a `paramLabel` for the option parameter to be used in the usage help message.
`boolean`	`required` Indicates whether this option is required.
`CommandLine.Help.Visibility`	`showDefaultValue` Use this attribute to control for a specific option whether its default value should be shown in the usage help message.
`java.lang.String`	`split` Specify a regular expression to use to split option parameter values before applying them to the field.
`java.lang.Class<?>[]`	`type` Optionally specify a `type` to control exactly what Class the option parameter should be converted to.
`boolean`	`usageHelp` Set `usageHelp=true` for the `--help` option that triggers display of the usage help message.
`boolean`	`versionHelp` Set `versionHelp=true` for the `--version` option that triggers display of the version information.

- Element Detail
  - names
```
public abstract java.lang.String[] names
```
    One or more option names. At least one option name is required.
    Different environments have different conventions for naming options, but usually options have a prefix that sets them apart from parameters. Picocli supports all of the below styles. The default separator is '=', but this can be configured.
    *nix
    In Unix and Linux, options have a short (single-character) name, a long name or both. Short options (POSIX style are single-character and are preceded by the '-' character, e.g., `-v'. GNU-style long (or mnemonic) options start with two dashes in a row, e.g., `--file'.
    Picocli supports the POSIX convention that short options can be grouped, with the last option optionally taking a parameter, which may be attached to the option name or separated by a space or a '=' character. The below examples are all equivalent:
```
 -xvfFILE
 -xvf FILE
 -xvf=FILE
 -xv --file FILE
 -xv --file=FILE
 -x -v --file FILE
 -x -v --file=FILE
 
```
    DOS
    DOS options mostly have upper case single-character names and start with a single slash '/' character. Option parameters are separated by a ':' character. Options cannot be grouped together but must be specified separately. For example:
```
 DIR /S /A:D /T:C
 
```
    PowerShell
    Windows PowerShell options generally are a word preceded by a single '-' character, e.g., `-Help'. Option parameters are separated by a space or by a ':' character.
    Returns:
    
    one or more option names
- - required
```
public abstract boolean required
```
    Indicates whether this option is required. By default this is false. If an option is required, but a user invokes the program without specifying the required option, a CommandLine.MissingParameterException is thrown from the CommandLine.parse(String...) method.
    
    Returns:
    
    whether this option is required
    
    Default:
    
    false
- - help
```
@Deprecated
public abstract boolean help
```
    Deprecated. Use usageHelp() and versionHelp() instead. See CommandLine.printHelpIfRequested(List, PrintStream, CommandLine.Help.Ansi)
    
    Set help=true if this option should disable validation of the remaining arguments: If the help option is specified, no error message is generated for missing required options.
    This attribute is useful for special options like help (-h and --help on unix, -? and -Help on Windows) or version (-V and --version on unix, -Version on Windows).
    
    Note that the CommandLine.parse(String...) method will not print help documentation. It will only set the value of the annotated field. It is the responsibility of the caller to inspect the annotated fields and take the appropriate action.
    
    Returns:
    
    whether this option disables validation of the other arguments
    
    Default:
    
    false
- - usageHelp
```
public abstract boolean usageHelp
```
    Set usageHelp=true for the --help option that triggers display of the usage help message. The convenience methods Commandline.call, Commandline.run, and Commandline.parseWithHandler(s) will automatically print usage help when an option with usageHelp=true was specified on the command line.
    By default, all options and positional parameters are included in the usage help message except when explicitly marked hidden.
    If this option is specified on the command line, picocli will not validate the remaining arguments (so no "missing required option" errors) and the CommandLine.isUsageHelpRequested() method will return true.
    Alternatively, consider annotating your command with @Command(mixinStandardHelpOptions = true).
    
    Returns:
    
    whether this option allows the user to request usage help
    
    Since:
    
    0.9.8
    
    See Also:
    
    hidden(), CommandLine.run(Runnable, String...), CommandLine.call(Callable, String...), CommandLine.parseWithHandler(IParseResultHandler2, String[]), CommandLine.printHelpIfRequested(List, PrintStream, PrintStream, Help.Ansi)
    
    Default:
    
    false
- - versionHelp
```
public abstract boolean versionHelp
```
    Set versionHelp=true for the --version option that triggers display of the version information. The convenience methods Commandline.call, Commandline.run, and Commandline.parseWithHandler(s) will automatically print version information when an option with versionHelp=true was specified on the command line.
    The version information string is obtained from the command's version annotation or from the version provider.
    If this option is specified on the command line, picocli will not validate the remaining arguments (so no "missing required option" errors) and the CommandLine.isUsageHelpRequested() method will return true.
    Alternatively, consider annotating your command with @Command(mixinStandardHelpOptions = true).
    
    Returns:
    
    whether this option allows the user to request version information
    
    Since:
    
    0.9.8
    
    See Also:
    
    hidden(), CommandLine.run(Runnable, String...), CommandLine.call(Callable, String...), CommandLine.parseWithHandler(IParseResultHandler2, String[]), CommandLine.printHelpIfRequested(List, PrintStream, PrintStream, Help.Ansi)
    
    Default:
    
    false
- - description
```
public abstract java.lang.String[] description
```
    Description of this option, used when generating the usage documentation.
    From picocli 3.2, the usage string may contain variables that are rendered when help is requested. The string ${DEFAULT-VALUE} is replaced with the default value of the option. This is regardless of the command's showDefaultValues setting or the option's showDefaultValue setting. The string ${COMPLETION-CANDIDATES} is replaced with the completion candidates generated by completionCandidates() in the description for this option. Also, embedded %n newline markers are converted to actual newlines.
    
    Returns:
    
    the description of this option
    
    Default:
    
    {}
- - arity
```
public abstract java.lang.String arity
```
    Specifies the minimum number of required parameters and the maximum number of accepted parameters. If an option declares a positive arity, and the user specifies an insufficient number of parameters on the command line, a CommandLine.MissingParameterException is thrown by the CommandLine.parse(String...) method.
    In many cases picocli can deduce the number of required parameters from the field's type. By default, flags (boolean options) have arity zero, and single-valued type fields (String, int, Integer, double, Double, File, Date, etc) have arity one. Generally, fields with types that cannot hold multiple values can omit the arity attribute.
    Fields used to capture options with arity two or higher should have a type that can hold multiple values, like arrays or Collections. See type() for strongly-typed Collection fields.
    For example, if an option has 2 required parameters and any number of optional parameters, specify @Option(names = "-example", arity = "2..*").
    A note on boolean options
    By default picocli does not expect boolean options (also called "flags" or "switches") to have a parameter. You can make a boolean option take a required parameter by annotating your field with arity="1". For example:
```
@Option(names = "-v", arity = "1") boolean verbose;
```
    Because this boolean field is defined with arity 1, the user must specify either <program> -v false or <program> -v true on the command line, or a CommandLine.MissingParameterException is thrown by the CommandLine.parse(String...) method.
    To make the boolean parameter possible but optional, define the field with arity = "0..1". For example:
```
@Option(names="-v", arity="0..1") boolean verbose;
```
    This will accept any of the below without throwing an exception:
```
 -v
 -v true
 -v false
 
```
    Returns:
    
    how many arguments this option requires
    
    Default:
    
    ""
- - paramLabel
```
public abstract java.lang.String paramLabel
```
    Specify a paramLabel for the option parameter to be used in the usage help message. If omitted, picocli uses the field name in fish brackets ('<' and '>') by default. Example:
```
class Example {
     @Option(names = {"-o", "--output"}, paramLabel="FILE", description="path of the output file")
     private File out;
     @Option(names = {"-j", "--jobs"}, arity="0..1", description="Allow N jobs at once; infinite jobs with no arg.")
     private int maxJobs = -1;
 }
```
    By default, the above gives a usage help message like the following:
```
 Usage: <main class> [OPTIONS]
 -o, --output FILE       path of the output file
 -j, --jobs [<maxJobs>]  Allow N jobs at once; infinite jobs with no arg.
 
```
    Returns:
    
    name of the option parameter used in the usage help message
    
    Default:
    
    ""
- - hideParamSyntax
```
public abstract boolean hideParamSyntax
```
    Returns whether usage syntax decorations around the paramLabel should be suppressed. The default is false: by default, the paramLabel is surrounded with '[' and ']' characters if the value is optional and followed by ellipses ("...") when multiple values can be specified.
    
    Since:
    
    3.6.0
    
    Default:
    
    false
- - type
```
public abstract java.lang.Class<?>[] type
```
    Optionally specify a type to control exactly what Class the option parameter should be converted to. This may be useful when the field type is an interface or an abstract class. For example, a field can be declared to have type java.lang.Number, and annotating @Option(type=Short.class) ensures that the option parameter value is converted to a Short before setting the field value.
    For array fields whose component type is an interface or abstract class, specify the concrete component type. For example, a field with type Number[] may be annotated with @Option(type=Short.class) to ensure that option parameter values are converted to Short before adding an element to the array.
    Picocli will use the CommandLine.ITypeConverter that is registered for the specified type to convert the raw String values before modifying the field value.
    Prior to 2.0, the type attribute was necessary for Collection and Map fields, but starting from 2.0 picocli will infer the component type from the generic type's type arguments. For example, for a field of type Map<TimeUnit, Long> picocli will know the option parameter should be split up in key=value pairs, where the key should be converted to a java.util.concurrent.TimeUnit enum value, and the value should be converted to a Long. No @Option(type=...) type attribute is required for this. For generic types with wildcards, picocli will take the specified upper or lower bound as the Class to convert to, unless the @Option annotation specifies an explicit type attribute.
    If the field type is a raw collection or a raw map, and you want it to contain other values than Strings, or if the generic type's type arguments are interfaces or abstract classes, you may specify a type attribute to control the Class that the option parameter should be converted to.
    
    Returns:
    
    the type(s) to convert the raw String values
    
    Default:
    
    {}
- - converter
```
public abstract java.lang.Class<? extends CommandLine.ITypeConverter<?>>[] converter
```
    Optionally specify one or more CommandLine.ITypeConverter classes to use to convert the command line argument into a strongly typed value (or key-value pair for map fields). This is useful when a particular field should use a custom conversion that is different from the normal conversion for the field's type.
    For example, for a specific field you may want to use a converter that maps the constant names defined in java.sql.Types to the int value of these constants, but any other int fields should not be affected by this and should continue to use the standard int converter that parses numeric values.
    
    Returns:
    
    the type converter(s) to use to convert String values to strongly typed values for this field
    
    See Also:
    
    CommandLine.registerConverter(Class, ITypeConverter)
    
    Default:
    
    {}
- - split
```
public abstract java.lang.String split
```
    Specify a regular expression to use to split option parameter values before applying them to the field. All elements resulting from the split are added to the array or Collection. Ignored for single-value fields.
    
    Returns:
    
    a regular expression to split option parameter values or "" if the value should not be split
    
    See Also:
    
    String.split(String)
    
    Default:
    
    ""
- - hidden
```
public abstract boolean hidden
```
    Set hidden=true if this option should not be included in the usage help message.
    
    Returns:
    
    whether this option should be excluded from the usage documentation
    
    Default:
    
    false
- - defaultValue
```
public abstract java.lang.String defaultValue
```
    Returns the default value of this option, before splitting and type conversion.
    
    Returns:
    
    a String that (after type conversion) will be used as the value for this option if no value was specified on the command line
    
    Since:
    
    3.2
    
    Default:
    
    "__no_default_value__"
- - showDefaultValue
```
public abstract CommandLine.Help.Visibility showDefaultValue
```
    Use this attribute to control for a specific option whether its default value should be shown in the usage help message. If not specified, the default value is only shown when the CommandLine.Command.showDefaultValues() is set true on the command. Use this attribute to specify whether the default value for this specific option should always be shown or never be shown, regardless of the command setting.
    Note that picocli 3.2 allows embedding default values anywhere in the description that ignores this setting.
    
    Returns:
    
    whether this option's default value should be shown in the usage help message
    
    Default:
    
    picocli.CommandLine.Help.Visibility.ON_DEMAND
- - completionCandidates
```
public abstract java.lang.Class<? extends java.lang.Iterable<java.lang.String>> completionCandidates
```
    Use this attribute to specify an Iterable<String> class that generates completion candidates for this option. For map fields, completion candidates should be in key=value form.
    Completion candidates are used in bash completion scripts generated by the picocli.AutoComplete class. Bash has special completion options to generate file names and host names, and the bash completion scripts generated by AutoComplete delegate to these bash built-ins for @Options whose type is java.io.File, java.nio.file.Path or java.net.InetAddress.
    For @Options whose type is a Java enum, AutoComplete can generate completion candidates from the type. For other types, use this attribute to specify completion candidates.
    
    Returns:
    
    a class whose instances can iterate over the completion candidates for this option
    
    Since:
    
    3.2
    
    See Also:
    
    CommandLine.IFactory
    
    Default:
    
    picocli.CommandLine.NoCompletionCandidates.class
- - interactive
```
public abstract boolean interactive
```
    Set interactive=true if this option will prompt the end user for a value (like a password). Only supported for single-value options (not arrays, collections or maps). When running on Java 6 or greater, this will use the Console.readPassword() API to get a value without echoing input to the console.
    
    Returns:
    
    whether this option prompts the end user for a value to be entered on the command line
    
    Since:
    
    3.5
    
    Default:
    
    false
- - descriptionKey
```
public abstract java.lang.String descriptionKey
```
    ResourceBundle key for this option. If not specified, (and a ResourceBundle exists for this command) an attempt is made to find the option description using any of the option names (without leading hyphens) as key.
    
    Since:
    
    3.6
    
    See Also:
    
    CommandLine.Model.OptionSpec.description()
    
    Default:
    
    ""

Annotation Type CommandLine.Option

Required Element Summary

Optional Element Summary

Element Detail

names

required

help

usageHelp

versionHelp

description

arity

paramLabel

hideParamSyntax

type

converter

split

hidden

defaultValue

showDefaultValue

completionCandidates

interactive

descriptionKey