Grep.java

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;

public class Grep {
	public static void main(String[] args) throws IOException {
		if(args.length != 2) {
			System.err.println("Wrong parameter count!");
			System.err.println("USAGE:\tjava Grep pattern file");
			System.exit(-1);
		}

		String re = ".*" + args[0] + ".*";
        	String filename = args[1];

		File file = new File(filename);
		BufferedReader in = new BufferedReader(new FileReader(file));
        	if(file.exists()) {
	            String line = null;
	            int lineNumber = 1;
	            while((line = in.readLine()) != null) {
	            	if (line.matches(re)) {
	            		System.out.println("L" + lineNumber + ": " + line);
	            	}
	            	lineNumber++;
	            }
	        }
	        in.close();
	}
}