Pool of oblivion

Checking for empty variables in PHP

2009-11-06T11:28:00.002+01:00

While writing some php code I checked for an empty string, using the empty() function, but I got this error :

PHP Fatal error: Can't use method return value in write context

I found this very strange because I've used the empty() function many times before. It turns out that the empty() function can not handle the return value of a function or method. You can only check variables using this function.

The solution is simple, store the return value of a function in a variable, and then check the variable with the empty() function :

wrong

if ( empty ( some_function() ) ) {

right

$some_variable = some_function();
if ( empty ( $some_variable ) ) {

On a side note, using the empty() function, is the best way to check for an empty variable, because it combines multiple checks, and works for different variable types. See documentation for details. When relying solely on strlen() or isset(), you can get an unexpected result.

New challenge

2009-10-03T14:36:00.016+02:00

About a year ago I started something that, a few days ago, came to a conclusion - but to be fair, it's more a milestone than a conclusion.
In August of last year (2008), I applied for a job at Ghent University. In the months that followed I went through the selection process, and after some hurdles I got selected. In April of this year (2009), I started on my new job. And now, six months later, my trial period is over. After a very good evaluation, I was appointed to the job, starting October 1st.
It took me over a year to get so far, but now I've reached what I was aiming for since then. But of course, this is just the start of it all. I have the rest of my life's working career ahead of me at Ghent University. And I'm still getting started, with a lot of plans to accomplish, projects to start, task being assigned, ... I'll know what to do the next few years.

But now that I've reached some stability on the work front, I might think of a new challenge, some new projects to start, or some overall reorganisation of the goals and priorities in my life. I've been thinking of a few, some silly or ridiculous, others infeasible (at least on my own), or down right impossible ways to pass time:

Find a way of solving any Rubik's cube in maximum 21 steps. The current proof says maximum 22 steps are needed.

Write a socio-philosophical essay addressing some effects of globalism : economy, environment, politics, communication, pluralism, culture, migration.

Now that, Gianfranco Gentile, a researcher of Ghent University has discovered that dark matter is needed to explain certain behavior in galaxies, it might be time to create a theory combining classic, relativistic and quantum mechanics together with dark matter.

Work on something revolutionary to save energy, use available energy more efficiently, not only by technology, but also by a change of mentality.

Build a render farm.

Start beatboxing.

Research methods of efficiently stacking solids, and by extension, deformable solids (f.e. a sealed bag containing a liquid).

But some are more realistic so I'll focus on those :

Learn to solve a Rubik's Cube. This is trivial, but I would like to find it by myself.

Pick up playing the piano again.

Read more, by which I mean : books, literature.

Or I could just try to look for goals in my work, find a girlfriend, buy a house, get married, start a family and raise some children.

Rename multiple tables in MySQL database

2009-03-11T20:00:00.012+01:00

Having to rename multiple tables with a similar pattern (prefix, suffix, ...) by replacing the recurring pattern, isn't an easy task, because there is no simple function or statement for doing it, not as far as I know.
Renaming tables like 'table_1234' and 'table_3456' to 'new_table_1234' and 'new_table_3456', is pretty straightforward in SQL:


RENAME TABLE `database`.`table_1234`
   TO `database`.`new_table_1234`;
RENAME TABLE `database`.`table_3456`
   TO `database`.`new_table_3456`;

or in one SQL statement :


RENAME TABLE
   `database`.`table_1234` TO `database`.`new_table_1234`,
   `database`.`table_3456` TO `database`.`new_table_3456`;

But when renaming a lot of tables, this method becomes tedious and time consuming.

This PHP script automates the renaming of multiple tables in a MySQL database. It lists all tables in a MySQL database, which contain a defined string pattern. The script creates and executes a series of SQL statements, which rename the table by replacing the search pattern in the original table name with another pattern in the new table name.

This script can easily be modified to rename multiple databases, or when stripping the original pattern (f.e. a prefix) and adding a new pattern (f.e. a suffix) is needed.


<?php
$db_server = "localhost";    // hostname MySQL server
$db_username = "username";   // username MySQL server
$db_password = "password";   // password MySQL server
$db_name = "database";       // database name

$pattern = "pattern_";          // search string
$new_pattern = "new_pattern_";  // replacement string, 
                                // can be empty

// login to MySQL server
$link = mysql_connect( $db_server, $db_username, $db_password);

if (!$link)
{
  die('Could not connect: ' . mysql_error());
}

// list all tables in the database containing the search pattern
$sql = "SHOW TABLES FROM `" . $db_name . "`";
$sql .= " LIKE '%" . $pattern . "%'";

$result = mysql_query ( $sql, $link );
if (!$result)
{
  die("Invalid query: " . mysql_error( $link ));
}

$renamed = 0;
$failed = 0;

while ( $row = mysql_fetch_array ($result) )
{
  // rename every table by replacing the search pattern 
  // with a new pattern
  $table_name = $row[0];
  $new_table_name = str_replace ( $pattern, $new_pattern, $table_name);

  $sql = "RENAME TABLE `" . $db_name . "`.`" . $table_name . "`";
  $sql .= " TO `" . $db_name . "`.`" . $new_table_name . "`";

  $result_rename = mysql_query ( $sql, $link );
  if ($result_rename)
  {
    echo "Table `" . $table_name . "` renamed to :`";
    echo $new_table_name . "`.\n";
    $renamed++;
  }
  else
  {
    // notify when the renaming failed and show reason why
    echo "Renaming of table `" . $table_name . "` has failed: ";
    echo mysql_error( $link ) . "\n";
    $failed++;
  }
}

echo $renamed . " tables were renamed, " . $failed . " failed.\n";

// close connection to MySQL server
mysql_close( $link );
?>

Syntax Highlighting in Blogger

2009-03-11T11:33:00.000+01:00

I've added some Javascript to the template of my blog to get Syntax Highlighting working. This means source code is formatted so it is easier to read. If it works allright, you should see an example of some highlighted php-code below. (The source code is not formatted/coloured when reading this post through an RSS-feed.)


<?php
/* Sample php code
This code doesn't do anything at all.
It just contains some php elements that should be formatted
and coloured.
*/

$some_variable = "some_string";

// Some comment
$result = some_function( $some_variable );

if (!$result)
{
  die("It doesn't work!");
}

$some_array = new array();

$some_array[0] = $result;
?>

Green Plug Universal Power Adaptor

2009-02-07T14:46:00.009+01:00

How many electronic devices do you have? A laptop, cell phone, MP3 player, external hard disc, GPS, ...
And each of them has its own adaptor, which can only be used with a specific device and isn't compatible with your other devices.
So you end up with several different adapters powering your devices, which results in a lot of cables that can get entangled, and which take up a lot of power plugs.
And if an adapter breaks, you have to buy a spare one from the original manufacturer, which costs a lot.

Wouldn't it be nice if there was a universal adapter for all your electronic devices?
You would only have to take one adaptor with you, to charge your cell phone, MP3 player and laptop. If a friend or colleague forgot to take her or his adapter, he or she could easily use yours, even if he or she uses a laptop of a different brand.

Actually, there is an initiative to standardize power adaptors :
Green Plug Universal Power Adaptor.

Enabling wireless network on an Acer Aspire One in Ubuntu

2009-01-12T16:56:00.003+01:00

I just installed Kubuntu 8.10 on an Acer Aspire One. Everything seems to work fine, but the wireless network doesn't seem to work.
Luckily I found this HOWTO on enabling the wifi.

Social Web

2008-11-21T14:26:00.007+01:00

Social networking websites are becoming more and more popular, and it's number is growing. Some websites provide a unique service, while other websites seem to be more of the same.
Some of your friends join one website while others join another, and both of them are requesting to join them on their website of choice.

After a while you have an account with several of those websites, and you start to notice you are providing the same information over and over again, on every of those websites : personal details, interests, schools you attended, employers you worked for.
And you have to (re)connect to your friends on every of those websites.
Not to mention when something changes, for instance when you change jobs, you have to change it on every website and hope you don't forget any of them.

Wouldn't it be convenient if all of the information you provide on those websites, can be shared between those websites? If you want to change something, you can do it in one place and all other social networking websites where you have an account adopt these changes automatically? If you add a friend on one website, and that friend has an account on another website where you have an account too, that this friend is added there as well?

I'm not the only one asking the same questions. And it seems some effort is put into creating a Social Web, where this kind of (personal) data can be shared between (social networking) websites in a open, easy and secure way.
These are a few of the initiatives :

Data Portability
Social Web Incubator Group (backed by W3C)
OpenSocial

A recent presentation (June 2008) was held with an overview of these efforts and what the future will bring. Unfortunately, these efforts, for now, are quite theoretical and about creating standards based upon existing web standards. Several protocols are proposed (FOAF, XFN, hCard, GRDDL, RDF, OpenID, OAuth, REST, ...) to be used in this new standards.

No real usable application is available at the moment, not as far as I know, but the big players (MySpace, Facebook, Google, Twitter, Netlog, ...) are backing some of these initiatives.

Noisy fan

2008-10-09T21:05:00.003+02:00

I noticed a whining noise, coming out of my computer, and it turned out to be caused by the fan on my graphics card. It is about 3 years old, so the fan starts to wear and will soon stop turning, which could be disastrous for the GPU on the graphics card.

So I started looking for a replacement fan on the producer's website and found this :

Noisy Fan or Fan Failure
The fans on ATI graphics cards are not user replaceable parts. To avoid any complications due to any possible damage that may have been caused by the fan's failure or degraded functionality, the entire card should be replaced. If the card is currently under warranty and built by ATI, you can fill out and submit the online warranty request form at http://www.ati.amd.com/rma.

As I mentioned, my graphics card, a ATI Radeon 9600 XT 128MB, is 3 years old, so past warranty, but it still works fine. It seems I'll have to find a replacement fan, without help from ATI. I'm sure I'll find one, but I'm a bit upset ATI provides such a lousy service.

I can understand, they want you to buy a completely new and costly graphics card that's faster and better, but maybe if you read something like this, a customer might consider buying a graphics card of another supplier next time. One that does provide spare fans. ;)

RIP Mark Hoekstra

2008-09-23T14:44:00.005+02:00

Mark Hoekstra, a young Dutch guy, passed away last week, after suffering a heart attack. He was only 34.

He hosted the geektechnique.org website, informing the world of his ongoing projects and hacking together of electronic gadgets.

His death is a great loss for the Open Source and hacking community.

RIP Mark Hoekstra, you will be missed.

Dreamjob

2008-08-15T14:23:00.003+02:00

Changing jobs is always some sort of a gamble. Will I like it? Is it as described in the vacancy? Is it as I expected it to be?
Therefor, it is important to know what you want and expect of a job.

Taking my current and past job experiences in account, this is what my ideal job would look like :

It should have something to do with technology or IT. I enjoy creating new things, so some programming, engineering or research should be envolved.

I have to believe in what I'm doing or what I'm being part of. The long-term project or product should be something I can support and be commited to. Maybe some sort of Open Source project, or cutting edge technology.

Considering my health, it is important I get enough sleep. Although I always enjoyed doing project work which involved long, irregular hours and traveling abroad, it's better for me if I can have less demanding hours.

I don't mind forensing, to a certain extent, but I'd like to live near where I work. Working in the same city where I live, is therefor preferrable. For a dreamjob, I would even consider relocating, even if it means going abroad.

The working atmosphere should be nice. Getting along with my colleagues is important as I'm around them for a major part of the day, and maybe even for a large part of my working life.

Retraining batteries

2008-08-04T11:24:00.003+02:00

I've bought an Apple iPod (4G) three years ago (December 2004) and I've noticed its battery life decreasing over the years.

A few months ago (March 2008) I started on a new job, for which I spend about 2-3 hours per day commuting by train, during which I listen to music on my iPod.
When I first started, I could use my iPod for 2 days (approx. 5 hours of listening), without recharging the battery. But over the past months, the battery life increased. Last week I managed to use my iPod for 4 consecutive days (approx. 10 hours of listening), without recharging. It seems that battery memory can be 'retrained'.

Todo list

2008-07-16T19:44:00.007+02:00

This post is a work in progress, listing things I would like to do in the near and more distant future.
Some may be completed soon, while others will take a long time or may never be completed.
While some items are in preparation of another item on the list, others have no set goal or defined purpose, yet. Thus, the items on this list are in no particular order :

Learning new programming languages and improving my knowledge of the ones I'm already familiar with :
- Erlang
- C++
- Perl
Linux :
- Finish the CLFS project for my old 486
- Upgrade to a new version of LFS on my server
- Get my encrypted external hard drive working in linux and windows
- Learn more about the linux kernel and maybe participate in its development or that of another Open Source project
Continue work on some small PHP-projects

Think about the feasibility of the semantic web, Turing tests, universal machines and time travel.

(Re)paint my bathroom

Find a new hobby

Get a girlfriend

What a week!

2008-02-23T15:42:00.008+01:00

Last week, I did a selection test at NMBS.
Yesterday, I got the result : 13,5/20, which is enough to go to the next round. But I'm not sure I will do the interview in the next round, given recent developments.

On Wednesday, I had another interview, this time for a job at VUB. Before I got home, they contacted me to announce I got the job. Since then I have made some arrangements to speed up the procedure for appointing my successor at my current job and got to an agreement with my new employer when to start working.

Today is my birthday. I've received a lot of messages, for which I'm grateful.
Tonight I will do something relaxing, going out for diner and maybe watch a film at the cinema.

Selection test #2 : trip to VUB

2008-02-20T21:05:00.005+01:00

I went, I told them what I know and I got a job!

This morning I went to Brussels, for the second time this week, for a job interview and written selection test, this time at VUB. The job I applied for is very similar to what I do now, i.e. system administration of linux servers.

The written test, in the morning, went well, explaining some linux and digital library terms and answering some sysadmin related questions. In the afternoon, I had an interview, with more questions about linux, libraries, me and my motivation. And although I was quite nervous, it went well.

On the way home, I got a call, telling me I was ranked first and congratulating me with my appointment as sysadmin.

I didn't expect to hear from them so soon. I thought it would take at least a day or two, before they would let me know the outcome of their deliberation. But it didn't take that long, so I'm very excited getting that job.

I have some thinking to do and arrange a few things, soon, as they would like me to start in March already.

Waiting for reactions

2008-02-18T21:43:00.009+01:00

As I'm actively looking for a new job, during the last few weeks, I've send out some applications already. But after sending them, comes a very boring and nerve-wrecking stage : waiting for reactions.

Some companies have a web application or a dedicated E-mail address for sending applications. Other have a good policy on handling applications. Both result in a (semi-)automatic answer, thanking you for your application, confirming your application was received or instructions on when to expect an answer (or not), or what to do when you haven't received an answer within a certain period of time.

Others send out letters or E-mails thanking you for your application, but regret to have to inform the vacancy is already filled or you don't seem to satisfy all the criteria needed for the job, wishing you good look on finding a job.
But, in case you're not suitable for the job, they never tell you why you're not fitting in. Was it something in the presentation letter? Was I too modest, or not elaborative enough? Did I write something offending? Didn't I apply to all courtesy and protocol which is needed in writing a presentation letter?
Or do I miss some experience or education? Did they put more value in the optional prerequisites, than was laid out in the vacancy?
I probably will never know, but it keeps me wondering.

But some don't react to your application at all, which is actually quite rude. If they would just send a short message informing you don't fit in (like I mentioned in the previous paragraph), you can stop waiting for an answer. But if no reaction comes, when can you stop hoping for a reaction?

But fortunately, you only need one job, so if you send out enough applications, some reach companies of the first type, resulting hopefully in a positive reaction or an invitation for further testing or an interview. And once you have a job, it doesn't matter some applications never get answered. But while you're waiting, it can be quite stressful.

Selection test #1.1

2008-02-17T15:15:00.006+01:00

Yesterday, I had to wake up early. 6:30 is early enough during the week, but on a Saturday it's even more unpleasant. The reason I had to get up this early, was because I had to be in Brussels at 9 o'clock to participate in a selection test for a new job.

Despite the early time, I managed to get out of bed, take a shower and eat some breakfast. Then I headed for the train station. Because I left a little early I managed to get a train earlier, giving me more time to get a connection at Gent-Sint-Pieters, on my way to Brussels South

The building where I was expected to take the test is near Brussels South, so I just had to cross the street to get there. Being a bit early, I had to wait in the hall, watching the other contestants arrive. At 8:50 we were let in, good thing I planned to take a train arriving at 8:30, because the next one arrived at 8:54 at the station, leaving me only minutes to locate the building, getting there and finding the entrance.

Before taking the test we got an introduction about the company, the kind of work we would have to do, once employed, and an overview of the selection procedure, which was about to start a few minutes later with a written selection test.

The written test was multiple choice, with 40 questions, divide in 3 categories. To discourage guessing answers, every wrong answer was penalized with 1/3 of a point. For every good answer one was awarded one point. In the end one had to score 10/20 to get to next round, which is an oral test.
The three categories were mechanics, electricity (common knowledge) and electricity ( power or signal ). It went rather well, considering that it has been some years now since I graduated and some of my knowledge of these topics is rather dusty. And I didn't have time to review everything before the test.
I managed to solve 28 of 40 questions, of which I'm quite certain.
So now it's waiting for the results. The oral test is planned in two weeks, which leaves me some time to review some more of my previous courses. If you catch me with a book on electrical motors, you'll know why.

BTW: Thanks to Tine, for letting me borrow a non-programmable calculator for this test.

Preparing for a new job

2008-02-15T17:37:00.007+01:00

I mentioned earlier that I decided to stop studying and start working again.
Last month I've been looking for job opportunities, sending applications and preparing for interviews and selection tests.
Tomorrow and next Wednesday I'm invited for selection tests. The test I'm taking tomorrow is for a technical job, which is in line with my bachelor diploma in electromechanics.
The test and interview on Wednesday is for a systems administration job (IT), managing computers and servers running Linux. It's a bit like the job I currently have at Ghent University.
I also made an appointment with my previous employer, to talk about a job offer.

Today I decided to quit my current job by the beginning of the Easter Holidays and start working on a new job, somewhere near 1st of April. I'm hopeful to find a suitable job by then.

So the next few weeks, I will be doing interviews, waiting for reactions, finding a successor for my current job at the university and finish some small projects.

Studying ex, working in

2008-01-06T22:05:00.000+01:00

Some close friends and family saw it coming, but I finally decided to stop studying. It's not that I'm no longer interested in physics, nor that I don't want to know more about it, but I can't bring myself to studying for exams anymore. I had a good time studying at the university and I have learned a lot over the past few years and I have met a lot of interesting people in this period, but it's time to go on and get to something else.

I've been looking around for the past few days, wondering which direction to take. I'm going back to working, that's for sure, but I have nearly endless possibilities. I can go back to my previous employer or the automation industry in general, but having gained some Linux, sysadmin and web development skills during the years I've spent at the university, I might as well apply for a job in that field as well.
I could look for a job in, or near, my hometown, but nothing is restricting me to go looking further, maybe even abroad.
Right now I'm looking what's available and feasible on the job market, in Belgium and abroad. I've started applying and probably will begin doing interviews soon. And I will continue to do so until I find a job that's best for me.
I'm not really in a hurry, so I can take my time evaluating the opportunities I come by and choose the most interesting one.

Growing a crystal #1

2007-11-13T21:34:00.000+01:00

Today, the professor handed out small bags with a white powder to me and my fellow students. As I mentioned before, I have to grow a crystal from a powder, for the professor's class. And today the powder arrived so I can start growing my crystal.

I went to the supermarket to get demineralised water. I can't use tap water, as this contains to much calcium and other substances that could affect the growing of the crystal.
Back home I mixed some powder with the water and stirred until the powder was completed dissolved. The liquid is clear again.
Then I added some more powder and mixed again, but this time not all of the powder is dissolved. That's normal as I calculated how much powder could be dissolved in the water at room temperature. By adding some more of the powder, the solution becomes saturated, thus it cannot dissolve more of the powder.

By heating the water a bit, the water can dissolved more of the powder. I put the beaker in the microwave for about 40 seconds and stirred again. Now all the powder, even the excess powder, is dissolved, resulting in a clear liquid.

When the water cools down to room temperature, the liquid remains clear, thus the solution contains more powder than it previously contained before heating. This means the solution is oversaturated. That is what is needed to start growing a crystal.

First I need a seed crystal, so I put a thin copper wire in the oversaturated liquid, in order to let a seed crystal grow on the wire.

Now I have to wait for the liquid to cool down further and let the seed crystal(s) grow. I'll check back in a few hours before I go to sleep, but I expect to see something when I wake up in the morning.

(I would post some pictures of the process, but I don't have a (digital) camera, so you'll have to believe what I'm describing)

Spooks series 6

2007-10-24T13:35:00.000+02:00

A pure work of art, absolutely brilliant. That's how I would describe the new episodes of BBC drama series Spooks, of which series 6 started last week on BBC1.

The first story spans the first two episodes. In the first episode, a threat of a fast spreading lethal virus in London is introduced. In the second episode it gets even more harsh, when MI5 decides to abduct spies of befriended nations like USA, Russia and France and threats to infect them with the virus, to persuade them to reveal the location of the antidote. MI5 believes one of those nations manufactured the virus and must have produced an antidote as well, but are certain the only way to get them to admit this antidote exists, is by these extreme measures.
In the end the antidote is found and all infected victims are cured, but relations with intelligence services of befriended nations are very hostile because of the abduction. And this will most definitely dominate the storyline of the next episodes. I'm really looking forward to it.

Priority

2007-10-14T16:44:00.000+02:00

Some time ago, I figured out I don't have enough time to spend on things I do, like doing and would like to do.
I realize it is impossible to create more time, so over the past few weeks I have come to the conclusion I need to be efficient at spending the available time and give priority to important and necessary things like sleeping and working.
As the academic year started a few weeks ago, I set a high priority to attending classes and studying as well, or this might be my last year as a student.
All others things, apart from spending time with friends and family, get a lower priority. This means I spend little to no time on certain activities, like attending meetings and staying up to speed with all details in the news. And some things I skipped totally, like going out during the week.

So the keyword in all this is priority, and acting according to it. This means I sometimes have to say no, or when I fail to do so, take the consequences by not being able to do something else.

Posting on this blog is one of the low priority things. It's not that there isn't anything to post about, but I lack the time and the motivation to write about it. When I feel like it, I will post something, if not, you can check the insert with shared news items on the right side of this blog. I add items regularly when I come along something that might be of some interest.

Physics : handywork

2007-09-27T17:53:00.000+02:00

In the exercises class of my Crystallography course, an assignment was given :

Craft a cube and bring it to class next week. It can be made of any material. You will need it to help you with the exercises.

So I cut a cube out of some insulation foam. But I'm not completely pleased with the result.
First I thought of making a cube from cardboard, by drawing some squares, cutting them from the cardboard and folding them together. But I figured this cardboard cube would be crushed when transported in my backpack, so I needed some structure that's not hollow.
Insulation foam is very light and relativily easy to sculpt, so I chose this material and started creating my cube, by measuring, cutting and sculpting. The end result looks like a cube, but not all sides are completely square. But it will do for the exercises.

This course starts to become some sort of handywork class, as in a few weeks we will be instructed to grow a crystal at home, starting from a beaker containing a dissolved substance. It's all very exciting. :-)

Archiving

2007-09-22T16:22:00.000+02:00

Next monday, a new academic year starts. This means : new courses and new lectures.
So it is time to archive some of my previous courses and make room for the new ones.

As it happened to be, there was still studying material of my first year Eastern Studies somewhere on a shelve. Because I won't need it anymore, I switched to physics and astronomy two years ago, I put it together in two small piles, made a list of the courses in each pile and bound them together with a string. The piles are now stored with the other archived studying material in another room.

With the old material out of the way, the courses of last year, which where on my desk, now take the free spot on the shelve, as I might want to look something up during the next two semesters.
The available space on my desk will soon be taken by the new studying material for next semester.

Shopping for clothing

2007-09-20T17:11:00.000+02:00

Today I went shopping in Antwerp, to buy some clothes. I left by train in Ghent at 13u13 and arrived in Antwerp about 45 minutes later. Then I went to 'De Meir', the biggest shopping street in Antwerp and bought the following things :

1 pair of shoelaces
3 trousers
4 T-shirts
3 pull-overs

I left again by train at 15u06.

The shopping spree took me under 3 hours, to buy enough clothes to have no need to going shopping for another year.

People might wonder why I went to Antwerp to buy clothes. If I would have shopped in Ghent, I might have spent even less time. The reason is simple : I like going to Antwerp once in a while, and the shop where I usually buy my clothes is bigger in Antwerp than the one in Ghent, so there are more clothes to choose from.

Search your feeds in Google Reader

2007-09-06T12:59:00.000+02:00

A long awaited search function is added to Google Reader.

Now you can search newsfeeds you previously read. If you know you read a newsitem about something, but can't remember on which feed it appeared, just search for it in Google Reader and the post will turn up.