Command Line Flags in CLIPS

Command-line flags are a common way to specify options for command-line programs. For example, in wc -l the -l is a command-line flag.

Java doesn’t have a built-in package for parsing command-line flags like Go’s flag package. However, we can use third-party libraries like Apache Commons CLI or write our own simple parser. For this example, we’ll use a simple custom implementation.

import java.util.HashMap;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class CommandLineFlags {
    public static void main(String[] args) {
        // We'll use a Map to store our flag values
        Map<String, String> flags = new HashMap<>();
        List<String> positionalArgs = new ArrayList<>();

        // Default values
        flags.put("word", "foo");
        flags.put("numb", "42");
        flags.put("fork", "false");
        flags.put("svar", "bar");

        // Parse command-line arguments
        for (int i = 0; i < args.length; i++) {
            String arg = args[i];
            if (arg.startsWith("--")) {
                String[] parts = arg.substring(2).split("=", 2);
                if (parts.length == 2) {
                    flags.put(parts[0], parts[1]);
                }
            } else {
                positionalArgs.add(arg);
            }
        }

        // Print the parsed options and trailing positional arguments
        System.out.println("word: " + flags.get("word"));
        System.out.println("numb: " + flags.get("numb"));
        System.out.println("fork: " + flags.get("fork"));
        System.out.println("svar: " + flags.get("svar"));
        System.out.println("tail: " + positionalArgs);
    }
}

To experiment with the command-line flags program, first compile it and then run the resulting class file directly.

$ javac CommandLineFlags.java

Try out the compiled program by first giving it values for all flags.

$ java CommandLineFlags --word=opt --numb=7 --fork=true --svar=flag
word: opt
numb: 7
fork: true
svar: flag
tail: []

Note that if you omit flags, they automatically take their default values.

$ java CommandLineFlags --word=opt
word: opt
numb: 42
fork: false
svar: bar
tail: []

Trailing positional arguments can be provided after any flags.

$ java CommandLineFlags --word=opt a1 a2 a3
word: opt
...
tail: [a1, a2, a3]

Unlike Go’s flag package, our simple implementation allows flags to appear anywhere in the command line. All non-flag arguments are treated as positional arguments.

$ java CommandLineFlags --word=opt a1 a2 a3 --numb=7
word: opt
numb: 7
fork: false
svar: bar
tail: [a1, a2, a3]

This simple implementation doesn’t provide automatic help text generation. For a more robust command-line parsing solution in Java, consider using libraries like Apache Commons CLI or JCommander.

Command Line Arguments in CLIPS

Context in CLIPS

Learn X By Example

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Command Line Flags in CLIPS