Using java as a shell language

I've been trying to find what shell language I like better as the 'glue' needed between real applications. I've used perl a lot in the past, experimenting with python and ruby now. But I don't want an interpreted language. I really want a compile time language.

So today I figured why not use java.

The main problem is that most scripts are easy to modify and don't require compiling. For example you start your python script with

#!/usr/bin/python

It would be nice if I could do the same for Java. Well now you can.

Introducing the 'JavaLoader'

import java.io.*;
class JavaLoader {
  public static void main(String[] args) throws Exception {
    String pwd = System.getProperty("user.dir");
    System.out.println( "Received argument " + args[0]);
    String javaFile = args[0];
    if (javaFile.startsWith("./"))
      javaFile = javaFile.replace("./","");

    // Find class file
    String className = (javaFile.split("\\."))[0];

    // Comment out the shebang line so we can compile it.
    RandomAccessFile file = new RandomAccessFile(javaFile, "rw");
    file.seek(0);
    file.write("//".getBytes());
    file.close();

    // Compile it
    executeCommand(String.format("javac -cp $CLASSPATH:%s %s",pwd,javaFile));

    //Run
    executeCommand(String.format("java -cp $CLASSPATH:%s %s",pwd,className));

    // Put back #! line.
    file = new RandomAccessFile(javaFile, "rw");
    file.seek(0);
    file.write("#!".getBytes());
    file.close();
  }
  public static void executeCommand(String cmd) throws Exception {
    System.out.println("Executing command: [" + cmd + "]");
    Process p = Runtime.getRuntime().exec(cmd);
    printStream(p.getInputStream());
    printStream(p.getErrorStream());
  }
  public static void printStream(InputStream is) throws Exception{
    BufferedReader input = new BufferedReader(new InputStreamReader(is));
    String line;
    while ((line = input.readLine()) != null) {
      System.out.println(line);
    }
    input.close();
  }
}

By using this you can now write a script like so:

#!/usr/bin/java JavaLoader

class my {

  public static void main(String[] args) {
    System.out.println ("my: from here I am in java");
  }
}

To execute you first need to make sure the JavaLoader is compiled and in your classpath. Then execute your script. My script was called my.java so I did:

[root@pioneer local]# ./my.java
Received argument ./my.java
Executing command: [javac -cp $CLASSPATH:/usr/local my.java]
Executing command: [java -cp $CLASSPATH:/usr/local my]
my: from here I am in java

This is great no more settling, I get to use Java everywhere now!