Category Archives: General

Todays bash lesson

Leave a reply

Today I noticed that a bash script I created a couple of weeks ago to calculate some log file statistics was no longer working properly.

The culprit was the following line:

REGEX=`printf "^%s %i %.2i:%.2i\n" ${MONTH} ${DAY} ${HOUR} ${TMP_MIN}`

This regular expression was designed to match lines that start with a certain date and time. Lines like following:

May 28 12:02

The regular expression was no longer matching the log file entries I wanted it to. The problem was the day value. When I wrote and tested the script the day was double digits. Now, at the beginning of a new month, the days are single digits. The log file I was analyzing pads the day field to always be two digits wide. Thus, the regular expression no longer matched the lines because there was an unexpected space. Figuring out what was broken and fixing the regular expression didn’t take long.

REGEX=`printf "^%s %2i %.2i:%.2i\n" ${MONTH} ${DAY} ${HOUR} ${TMP_MIN}`

The script now worked properly but I noticed something weird. I had added a debugging statement below the REGEX definition.

echo ${REGEX}

This debugging statement was printing the regular expression with one space between the month and day, not the expected two. Yet, the script appeared to work perfectly. What was going on?

In trying to figure this out I went as far as creating a quick C program so that I could see exactly what was being passed in as the arguments.

Of course, it turned out to be something that should have been obvious. The bash echo command prints out each of the passed arguments with a single space between them. The echo command was interpreting each part of the string in the REGEX variable as an individual argument. The ‘fix’ was to enclose the bash variable in quotes so that it would be considered a single argument.

echo "${REGEX}"

Bash programming rule #x:: Always put double quotes around variables.

IPv6 address usage

Leave a reply

I stumbled upon a fabulous article that discusses address utilization in IPv4 and IPv6. Two aspects of this article struck me most: wrapping your head around really big numbers is hard and it is sad to see that some of the same mistakes made during the early days of IPv4 address allocations may be repeated.

Just how big is IPv6?

Red Hat Magazine

Leave a reply

Red Hat puts out a monthly publication called Red Hat magazine. It is usually worth looking at. Often they discuss new technologies that are entering RHEL or Fedora.

This month some of the articles include video presentations. However, the video is only available in Real Video or Quicktime. These codecs do not ship with Fedora; I’m not sure if they ship with RHEL.

Bad Red Hat!

Sin City

Leave a reply

Last Friday Karen and I went to see Sin City. Since then I have made several attempts to write about it without success.

I’m still a little stunned by this movie. Its scary, disturbing but yet funny at times. The bad guys are sometimes just lowly hit-men out to make a buck; others include cannibals and child molesters. Make no mistake, this movie hits all the evil person buttons. The good guys are still bad guys but do bad things for mostly good reasons.

Sin City is violent but the violence forms a big part of the world so it doesn’t seem out of place.

About the only conclusive thing I can say about this movie is that it is the most unique movie I have ever seen. For that reason alone, you should go see it too.

Update: I forgot to add one of my favourite quotes from the movie.

”I love hitmen. No matter what you do to ’em, you never feel bad.”
— Marv (Mickey Rourke)

It’s been a long time..

Leave a reply

Wow, it’s been a long time since I have posted. So here is a grab bag of what has been going on.

The last semester of my undergraduate degree is almost over. Less than two weeks left.

I handed in my undergraduate thesis last week; the presentation is this Tuesday. Fortunately, I was able to get the main work of the project done a couple of weeks ago which left me with lots of time to write the final report. This is good because I am a slow writer. At some point I’ll probably post a PDF version of the report here. If you are considering doing an undergraduate thesis I certainly recommend it. It is really great to be able to work on something personally interesting and get credit for it. Of course that is the catch, if your not interested in the topic, it is probably very hard to force yourself to do the required work.

After the thesis presentation on Tuesday the only course work I have left is two assignments: one for distributed systems and one for cryptography.

Also on the university front, I received my acceptance to the MSc program a few weeks ago.

Starting my MSc in September will be exciting but for now I’m just looking forward to four months with no homework. I’m pretty much at the burnout point.

One goal I have for the summer (besides being outside a lot) is to catch up on my reading. I tend to get quite far behind during the school year. In order to catch up I have to read: 6 issues Communications of the ACM, 5 issues of Linux Journal, 2 issues of IEEE/ACM Transactions on Networking, 5 issues of Queue and a few other miscellaneous magazines. Plus all of the unread books that have been accumulating.

And of course, some blogging!

Blog spam

Leave a reply

The blog spam on my site has gotten so bad I decided to use WordPress 1.5’s new word black list feature. It seems that 90% of the spam I get is for online casinos. These posts always contain either “texas holdem” or “poker” so I have black listed “holdem” and “poker”. This is a pretty big stick that I don’t want to use but constantly deleting spam in the moderation queue is getting quite annoying.

LQL# HTB control

Leave a reply

Now that LQL-Sharp has been released I thought I should put together a quick little demonstration of just how cool it is.

I have created a extremely simple GUI control that can modify the rate and ceiling parameters of a HTB class. This control should really subclass Gtk.Widget but it serves its purpose as is.

TC HTB Control

using System;
using Gtk;
using LQL;
class HTBControl {
	private LQL.ClassHTB klass;
	private LQL.Con con;
	private Gtk.SpinButton rateSpin;
	private Gtk.SpinButton ceilSpin;
	public HTBControl(LQL.ClassHTB klass, LQL.Con con)
	{
		this.klass = klass;
		this.con = con;
		Gtk.Window myWin = new Gtk.Window("TC GTK+");
		myWin.DeleteEvent += new DeleteEventHandler(WindowDelete);
		Gtk.VBox vbox = new Gtk.VBox(false, 3);
		Gtk.HBox hbox1 = new Gtk.HBox(false, 2);
		hbox1.Add(new Gtk.Label("Rate (bytes/sec): "));
		this.rateSpin = new Gtk.SpinButton(0, 10000000, 1);
		hbox1.Add(this.rateSpin);
		vbox.Add(hbox1);
		Gtk.HBox hbox2 = new Gtk.HBox(false, 2);
		hbox2.Add(new Gtk.Label("Ceiling (bytes/sec): "));		
		this.ceilSpin = new Gtk.SpinButton(0, 10000000, 1);
		hbox2.Add(this.ceilSpin);
		vbox.Add(hbox2);
		Gtk.Button modifyButton = new Gtk.Button("Modify");
		modifyButton.Clicked += new EventHandler(Modify);
		vbox.Add(modifyButton);
		rateSpin.Value = this.klass.Rate;
		ceilSpin.Value = this.klass.Ceiling;
		myWin.Add(vbox);
		myWin.ShowAll();
	}
	static void WindowDelete(object o, DeleteEventArgs args)
	{
		Gtk.Application.Quit();
		args.RetVal = true;
	}
	void Modify(object o, EventArgs args)
	{
		this.klass.Rate = (uint) this.rateSpin.Value;
		this.klass.Ceiling = (uint) this.ceilSpin.Value;
		this.klass.Modify(this.con);
	}
}
using System;
using Gtk;
using LQL;
class MainClass {
	public static void Main(string[] args)
	{
		Application.Init();
		LQL.Con con = new LQL.Con();
		LQL.Interface nIf = con.FindInterfaceByName("eth0");
		GLib.List classes = con.ListClasses(nIf);
		foreach (LQL.Class klass in classes) {
			if (klass is LQL.ClassHTB) {
				new HTBControl((LQL.ClassHTB) klass, con);
			}
		}
		Application.Run();
	}
}

LQL#

1 Reply

Work has begun on the long promised Mono (C#) bindings for LQL. This little C# program will display traffic statistics for all of the queueing disciplines that are supported by the C LQL library.

using System;
using LQL;
class MainClass {
    public static void Main(string[] args) {
        Gtk.Application.Init();
        LQL.Con con = new LQL.Con();
        GLib.List ifList = con.ListInterfaces();
        foreach (LQL.Interface netInf in ifList) {
            GLib.List qdiscList = con.ListQdiscs(netInf);
            foreach (LQL.QDisc qdisc in qdiscList) {
                qdisc.UpdateStats(con);
                qdisc.PrintStats();
            }
        }
    }
}

Very exciting stuff!

LQL# is not nearly polished enough for a public release yet but I am quite happy with how the work is progressing.