java-cli-arg-parser

A lightweight, zero-dependency command-line argument parser for Java. Supports boolean flags, value-taking options (--opt=value or --opt value), short aliases (-v for --verbose), positional arguments, an -- end-of-options marker, and generated --help text. Pure Java 17, no external libraries, no build tool required.

JAVAC="/path/to/jdk/bin/javac"
JAVA="/path/to/jdk/bin/java"

# Compile the library
"$JAVAC" -d out $(find src/main/java -name "*.java")

# Compile the tests against the compiled library
"$JAVAC" -cp out -d out $(find src/test/java -name "*.java")

# Run the tests
"$JAVA" -cp out dev.kasapdev.argparser.ArgParserTest

On Windows, replace $(find ... -name "*.java") with an explicit file list, or run the find substitution from Git Bash / WSL.

import dev.kasapdev.argparser.ArgParser;
import dev.kasapdev.argparser.ParsedArgs;
import dev.kasapdev.argparser.ArgParseException;

public class Example {
    public static void main(String[] args) {
        ArgParser parser = new ArgParser()
                .addFlag("verbose", "v", "Enable verbose output")
                .addOption("output", "o", "Output file path", "out.txt")
                .addOption("format", "Output format (json|csv)", "json");

        try {
            ParsedArgs parsed = parser.parse(args);

            if (parsed.flag("verbose")) {
                System.out.println("Verbose mode on");
            }
            System.out.println("Output file: " + parsed.option("output"));
            System.out.println("Format: " + parsed.option("format"));
            System.out.println("Positional args: " + parsed.positionals());
        } catch (ArgParseException e) {
            System.err.println("Error: " + e.getMessage());
            System.err.println(parser.helpText());
        }
    }
}

Running with input.csv --verbose -o result.json yields verbose=true, output=result.json, format=json (default), and positionals=["input.csv"].

• ArgParser addFlag(String name, String description) / addFlag(String name, String shortAlias, String description) — registers a boolean flag.
• ArgParser addOption(String name, String description, String defaultValue) / addOption(String name, String shortAlias, String description, String defaultValue) — registers a value-taking option with a default.
• ParsedArgs parse(String[] args) — parses the given arguments; throws ArgParseException naming the offending token on an unrecognized --flag/-f or a missing option value.
• String helpText() — generated help listing every registered option, its alias, and default value.

• boolean flag(String name) — whether the flag was present.
• String option(String name) — the supplied value, or the registered default.
• List<String> positionals() — positional arguments, in order.

MIT — see LICENSE.