mkavanagh/picocli

Annotation-based Java command line parsing library. Usage help with ANSI colors. Autocomplete. Nested subcommands. Easily included as source to avoid adding dependencies.

picocli - a mighty tiny command line interface

Annotation-based Java command line parser, featuring usage help with ANSI colors, autocomplete and nested subcommands. In a single file, so you can include it in source form. This lets users run picocli-based applications without requiring picocli as an external dependency.

How it works: annotate your class and picocli initializes it from the command line arguments, converting the input to strongly typed data. Supports git-like subcommands (and nested sub-subcommands), any option prefix style, POSIX-style grouped short options, custom type converters and more. Parser tracing facilitates troubleshooting.

Distinguishes between named options and positional parameters and allows both to be strongly typed. Multi-valued fields can specify an exact number of parameters or a range (e.g., 0..*, 1..2). Supports Map options like -Dkey1=val1 -Dkey2=val2, where both key and value can be strongly typed.

Generates polished and easily tailored usage help and version help, using ANSI colors where possible. Works with Java 5 or higher (but is designed to facilitate the use of Java 8 lambdas).

Picocli-based command line applications can have TAB autocompletion, interactively showing users what options and subcommands are available.

• Releases - latest: 2.0.3
• Picocli 2.0 Release Notes - including some potential breaking changes
• User manual: http://picocli.info
• Command line autocompletion
• API Javadoc
• FAQ
• Announcing picocli 1.0
• Picocli 2.0: Do More With Less
• Picocli 2.0: Groovy Scripts on Steroids
• Check out Thibaud Lepretre's picocli Spring boot starter!

Example

Annotate fields with the command line parameter names and description.

import picocli.CommandLine.Option;
import picocli.CommandLine.Parameters;
import java.io.File;

public class Example {
    @Option(names = { "-v", "--verbose" }, description = "Be verbose.")
    private boolean verbose = false;

    @Option(names = { "-h", "--help" }, usageHelp = true,
            description = "Displays this help message and quits.")
    private boolean helpRequested = false;

    @Parameters(arity = "1..*", paramLabel = "FILE", description = "File(s) to process.")
    private File[] inputFiles;
    ...
}

Then invoke CommandLine.populateCommand with the command line parameters and an object you want to initialize.

String[] args = { "-v", "inputFile1", "inputFile2" };
Example app = CommandLine.populateCommand(new Example(), args);

assert !app.helpRequested;
assert  app.verbose;
assert  app.inputFiles != null && app.inputFiles.length == 2;

Invoke CommandLine.usage if the user requested help or the input was invalid and a ParameterException was thrown.

CommandLine.usage(new Example(), System.out);

Usage Help with ANSI Colors and Styles

Colors, styles, headers, footers and section headings are easily customized with annotations. For example:

See the source code.

Usage Help API

Picocli annotations offer many ways to customize the usage help message.

If annotations are not sufficient, you can use picocli's Help API to customize even further. For example, your application can generate help like this with a custom layout:

See the source code.