How to print specific lines out of a Tail - N command.

Question

Hello,
Here is my problem. Within a web application, one of the menu is supposed to do the following:
Check the n lastest lines of a file (a log file in fact) and print the lines that only contain "ADD" or "DEL"
I don't know how to do it ! Please, help !!

Answer 1

This should get you started, it's a java version of tail which takes multiple files and there roll extension and runs forever (hopefully!).
* @author Jeff Hackert, Jon Strabala
import java.io.*;
import java.util.*;
public class TailIt extends Thread {
    private BufferedReader br = null;
    private Thread thread;
    private long rollTime = 0L;
    private String fname = null; // the log file
    private String rname = null; // the rolled log file
    private static boolean debug = false;
    private static synchronized void stdOut(String line) {
        System.out.println(line);
    public void run() {
        String s = null;
        boolean attail = false;
        long prev = System.currentTimeMillis();
        try {
            for(;;) {
                s = br.readLine();
                if ( s != null ) {
                    if (attail) {
                        TailIt.stdOut(s);
                } else {
                    attail = true;
                    try {
                        sleep(10);
                        long now = System.currentTimeMillis();
                        if (now > prev + 5000) { // checks roll every five seconds
                            prev = now;
                            checkRoll();
                    } catch (InterruptedException ioe) {}
                yield();
        } catch (IOException ioe) {}
    public void setRollTime() {
        File f = new File(fname);
        if (f.exists()) {
            rollTime = f.lastModified();
        } else {
            rollTime = 0;
    public void checkRoll() {
        long tmpTime = 0L;
        File f = new File(rname);
        if (f.exists()) {
            tmpTime = f.lastModified();
        if (rollTime < tmpTime) { //a roll occurred
            Date d = new Date(rollTime);
            stdOut("Log " + fname + " rolled at " + d.toString());
            try {
                br.close();
                br = new BufferedReader(new FileReader(fname));
            } catch (Exception e) {}
            setRollTime();
        } else {
            if (debug) System.err.println("no roll at " + rollTime + " " + tmpTime);
    public static void main(String [] args) {
        if (args.length != 0) {
            for (int i = 0; i < args.length; i = (i + 2)) {
                if ((i + 1) == args.length) {
                    System.err.println("Usage: TailIt <log file> <roll extension> ...");
                    System.exit(0);
                TailIt m = new TailIt();
                try {
                    m.fname = args;
m.br = new BufferedReader(new FileReader(m.fname));
m.rname = m.fname + "." + args[i + 1];
m.setRollTime();
m.thread = new Thread(m);
m.thread.start();
} catch (FileNotFoundException e) {
System.err.println(e);
} else {
System.err.println("Usage: TailIt <filename> <roll extension> <filename> <roll extension> ...");