Java the Script

demo.sh

$ ./java-the-script
Usage: ./java-the-script -e JAVA_CODE
    -i, --import PACKAGE             import PACKAGE before compiling code
        --debug                      debug mode: print the generated Java source
    -e JAVA_CODE                     Java source to compile and run
    -h, --help                       Show this message
$ echo "wooooo" | ./java-the-script -e 'System.out.println(STDIN.read().toUpperCase());'
WOOOOO
$ ./java-the-script -i java.util.Calendar -e 'System.out.println(Calendar.getInstance().get(Calendar.YEAR));'
2014

java-the-script

#!/usr/bin/env ruby
require 'optparse'
require 'tmpdir'

java_code = ""
imports = []
print_usage = false
debug_mode = false

parser = OptionParser.new do |opts|
  opts.banner = "Usage: #{$0} -e JAVA_CODE"

  opts.on('-i', '--import PACKAGE', 'import PACKAGE before compiling code') do |lib|
    imports << lib
  end

  opts.on('--debug', 'debug mode: print the generated Java source') do
    debug_mode = true
  end

  opts.on('-e JAVA_CODE', 'Java source to compile and run') do |java_expr|
    java_code = java_expr
  end

  opts.on_tail('-h', '--help', 'Show this message') do
    print_usage = true
  end
end

parser.parse!(ARGV)

if java_code.empty? || print_usage
  puts parser
  exit 1
end

imports << 'java.io.BufferedReader'
imports << 'java.io.InputStream'
imports << 'java.io.InputStreamReader'
imports << 'java.io.IOException'

import_declarations = imports.map do |import|
  "import #{import};"
end.join("\n")

if !java_code.end_with?(';')
  java_code << ';'
end

java_source = <<JAVA
#{import_declarations}

public class JavaTheScript {
  public static class StandardIn {
    private final BufferedReader reader;

    public StandardIn(InputStream in) {
      reader = new BufferedReader(new InputStreamReader(System.in));;
    }

    public String read() {
      StringBuilder builder = new StringBuilder();
      try {
        while (reader.ready()) {
          builder.append(reader.readLine());
        }
      } catch (IOException ex) {
        // chillin.
      }
      return builder.toString();
    }

    public String readLine() {
      try {
        return reader.readLine();
      } catch (IOException ex) {
        return "";
      }
    }
  }

  public static void main(String[] args) {
    StandardIn STDIN = new StandardIn(System.in);
    #{java_code}
  }
}
JAVA

if debug_mode
  puts java_source
  exit 0
end

Dir.mktmpdir do |dir|
  Dir.chdir(dir) do
    java_filename = 'JavaTheScript.java'
    File.open(java_filename, 'w') { |f| f.write java_source }
    system("javac", java_filename)
    exec("java", "JavaTheScript")
  end
end