[patch] add --init

build.gradle

@@ -19,6 +19,7 @@ dependencies {
 	implementation 'com.offbytwo:docopt:0.6.0.20150202'
 
 	implementation 'info.picocli:picocli:4.1.4'
+	//implementation 'io.quarkus.qute:qute-core:1.1.0.Final'
 
 	implementation("com.jcabi:jcabi-aether:0.10.1") {
 		exclude group: "org.hibernate", module: "hibernate-validator"

readme.adoc

@@ -79,6 +79,10 @@ chmod +x helloworld.java
 There are experimental support to run `.jsh` via `jshell`. The advantage of `jshell` is that you do not need to have a class or static main method, downside is that
 at least for now you have no way to read the command line arguments.
 
+## Getting started
+
+To get started you can run `jbang --init helloworld.java` and a simple java class with a static main is generated.
+
 ## Declare dependencies with `//DEPS`
 
 If you want to write real scripts you will want to use some java libraries.

src/main/java/dk/xam/jbang/ExitException.java

@@ -11,6 +11,11 @@ public ExitException(int status) {
 		this.status = status;
 	}
 
+	public ExitException(int status, Exception cause) {
+		super(cause);
+		this.status = status;
+	}
+
 	public int getStatus() {
 		return status;
 	}

src/main/java/dk/xam/jbang/Main.java

@@ -3,9 +3,8 @@
 import static java.lang.System.*;
 import static picocli.CommandLine.*;
 
-import java.io.File;
-import java.io.FileNotFoundException;
-import java.io.PrintWriter;
+import java.io.*;
+import java.nio.file.Files;
 import java.util.*;
 import java.util.concurrent.Callable;
 import java.util.stream.Collectors;
@@ -34,6 +33,9 @@ public class Main implements Callable<Integer> {
 	@Parameters(index = "1..*", arity = "0..*", description = "Parameters to pass on to the script")
 	List<String> params = new ArrayList<String>();
 
+	@Option(names = {"--init"}, description = "Init script with a java class useful for scripting.")
+	boolean initScript;
+
 	void info(String msg) {
 		spec.commandLine().getErr().println(msg);
 	}
@@ -65,7 +67,7 @@ static CommandLine getCommandLine() {
 	}
 
 	@Override
-	public Integer call() throws FileNotFoundException {
+	public Integer call() throws IOException {
 
 		if (helpRequested) {
 			spec.commandLine().usage(err);
@@ -75,13 +77,46 @@ public Integer call() throws FileNotFoundException {
 			quit(0);
 		}
 
-		String cmdline = generateCommandLine();
+		if (initScript) {
+			var f = new File(scriptOrFile);
+			if (f.exists()) {
+				warn("File " + f + " already exists. Will not initialize.");
+			} else {
+				// Use try-with-resource to get auto-closeable writer instance
+				try (BufferedWriter writer = Files.newBufferedWriter(f.toPath())) {
+					String result = renderInitClass(f);
+					writer.write(result);
+				}
+			}
 
-		out.println(cmdline);
+		} else {
+			String cmdline = generateCommandLine();
 
+			out.println(cmdline);
+		}
 		return 0;
 	}
 
+	static String initTemplate = "//usr/bin/env jbang \"$0\" \"$@\" ; exit $?\n"
+			+ "// //DEPS <dependency1> <dependency2>\n" + "\n" + "import static java.lang.System.*;\n" + "\n"
+			+ "public class {className} {\n" + "\n" + "    public static void main(String... args) {\n"
+			+ "        out.println(\"Hello World\");\n" + "    }\n" + "}";
+
+	String renderInitClass(File f) {
+
+		return initTemplate.replace("{className}", getBaseName(f.getName()));
+
+	}
+
+	public static String getBaseName(String fileName) {
+		int index = fileName.lastIndexOf('.');
+		if (index == -1) {
+			return fileName;
+		} else {
+			return fileName.substring(0, index);
+		}
+	}
+
 	String generateCommandLine() throws FileNotFoundException {
 		prepareScript = prepareScript(scriptOrFile);
 

src/test/java/dk/xam/jbang/TestInit.java

@@ -0,0 +1,22 @@
+package dk.xam.jbang;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.*;
+
+import java.io.File;
+
+import org.junit.jupiter.api.Test;
+
+public class TestInit {
+
+	@Test
+	void testInit() {
+
+		var m = new Main();
+
+		String s = m.renderInitClass(new File("test.java"));
+
+		assertThat(s, not(containsString("NOT_FOUND")));
+
+	}
+}

src/test/java/dk/xam/jbang/TestMain.java

@@ -86,6 +86,6 @@ void testDependencies() throws FileNotFoundException {
 		assertThat(result, not(containsString("  ")));
 		assertThat(result, containsString("classpath"));
 		assertThat(result, containsString("log4j"));
-	}
+	} 
 
 }