Tag Archive for Perl

JavaScript: write it yourself or use a library?

July 3, 2008 No comments

I must admit that I have never been a great fan of JavaScript. For one thing, its need to interact with browser objects places you at the mercy of the purveyors of such pieces of software. Debugging is another fine art that can seem opaque to the the uninitiated since the amount and quality of the logging is determined an interpreter that isn’t provided by the language’s overseers. All in all, it seems to present a steep and obstacle-strewn learning curve to newcomers. As it happens, I have always found server side scripting languages like PHP and Perl to be more to my taste and I have no aversion at all to writing SQL.

In the late 1990′s when I was still using free web hosting, JavaScript probably was the best option for my then new online photo gallery. Whatever was the truth, it certainly was the way that I went. Learning Java or Flash might have been useful but I never managed to devote sufficient time to the task so JavaScript turned out to be the way forward until I got a taste of server side scripting. Moving to paid hosting allowed for that to develop and the JavaScript option took a back seat.

Based on my experience of the browser wars and working with JavaScript throughout their existence, I was more than a little surprised at the buzz surrounding AJAX. Ploughing part of the way through WROX’s Beginning AJAX did nothing to sell the technology to me; it came across as a very dry jargon-blighted read. Nevertheless, I do see the advantages of web applications being as responsive as their desktop equivalents but AJAX doesn’t always guarantee this; as someone that has seen such applications crawling on IE6, I can certainly vouch for this. In fact, I suspect that may be behind the appearance of technologies such as AIR and Silverlight so JavaScript may get usurped yet again, just like my move to a photo gallery powered on the server side.

Even with these concerns, using JavaScript to add a spot more interactivity is never a bad thing even if it can be overdone, hence the speed problems that I have witnessed. In fact, I have been known to use DOM scripting but I need to have the use in mind before I can experiment with a technology; I cannot do it the other way around. Nevertheless, I am keen to see what JavaScript libraries such as jQuery and Prototype might have to offer (both have been used in WordPress). I have happened on their respective websites so they might make good places to start and who knows where my curiosity might take me?

Scripting, Web Development, Web Technologies

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A case of “peekaboo” behaviour in Internet Explorer

July 1, 2008 One comment

I recently changed the engine of my online photo gallery to a speedier PHP/MySQL based affair from its PHP/Perl/XML powered predecessor. On the server side, all was well but a peculiar display issue turned up in Internet Explorer (6, 7 & 8 were afflicted by this behaviour) where photo caption text on the thumbnail gallery pages was being displayed erratically. As far as I can gather, the trigger for the behaviour was that the thumbnail block was placed within a DIV floated using CSS that touched another DIV that cleared the floating behaviour. I use a table to hold the images and their associated captions in place. Furthermore, each caption was also a hyperlink nested within a set of P tags. The remedy was to set the CSS Display property for the affected XHTML tag to a value of "inline-block". With a cascade of DIV, TABLE, TR, TD, P and A tags, finding the right tag where the CSS property in question has the desired effect took some doing. As it happened, it was the tag set, that for the hyperlink, at the bottom of the stack that needed the fix. Of course, it’s all very fine fixing something for one browser but it’s worthless if it breaks the presentation in other browsers. In that vein, I did some testing in Opera, Firefox, Seamonkey and Safari to check if all was well and it was. There may be older browsers like versions of IE prior to 6 where things don’t appear as intended but I get the impression from my visitor statistics that the newer variants hold sway anyway. All in all, it was a useful lesson learnt and that’s never a bad thing.

Web Development

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A collection of lessons learnt about web hosting

March 28, 2008 No comments

Putting this blog back on its feet after a spot of web hosting bother caused me to learnt a bit more about web hosting than I  otherwise might have done. Here’s a selection and they are in no particular order:

  1. Store your passwords securely and where you can find them because you never know how a foul up of your own making can strike. For example, a faux pas with a configuration file is all that’s needed to cause havoc for a database site such as a WordPress blog. After all, nobody’s perfect and your hosting provider may not get you out of trouble as quickly as you might like.
  2. Get a MySQL database or equivalent as part of your package rather than buying one separately. If your provider allows a trial period, then changing from one package to another could be cheaper and easier than if you bought a separate database and needed to jettison it because you changed from, say, a Windows package to a Linux one or vice versa.
  3. It might be an idea to avoid a reseller unless the service being offered is something special. Going for the sake of lower cost can be a false economy and it might be better to cut out the middleman altogether and go direct to their provider. Being able to distinguish a reseller from a real web host would be nice but I don’t see that ever becoming a reality; it is hardly in resellers’ interests, after all.
  4. Should you stick with a provider that takes several days to resolve a serious outage? The previous host of this blog had a major MySQL server outage that lasted for up to three days and seeing that was one of the factors that made me turn tail to go to a more trusted provider that I have used for a number of years. The smoothness of the account creation process might be another point worthy of consideration.
  5. Sluggish system support really can frustrate, especially if there is no telephone support provided and the online ticketing system seems to take forever to deliver solutions. I would advise strongly that a host who offers a helpline is a much better option than someone who doesn’t. Saying all of that, I think that it’s best to be patient and, when your website is offline, that might not be as easy you’d hope it to be.
  6. Setting up hosting or changing from one provider to another can take a number of days because of all that needs doing. So, it’s best to allow for this and plan ahead. Account creation can be very quick but setting up the website can take time while domain name transfer can take up to 24 hours.
  7. It might not take the same amount of time to set up Windows hosting as its Linux equivalent. I don’t know if my experience was typical but I have found that the same provider set up Linux hosting far quicker (within 30 minutes) than it did for a Windows-based package (several hours).
  8. Be careful what package you select; it can be easy to pick the wrong one depending on how your host’s sight is laid out and what they are promoting at the time.
  9. You can have a Perl/PHP/MySQL site working on Windows, even with IIS being used in place instead of Apache. The Linux/Apache/Perl/PHP/MySQL approach might still be better, though.
  10. The Windows option allows for ASP, .Net and other such Microsoft technologies to be used. I have to say that my experience and preference is for open source technologies so Linux is my mainstay but learning about the other side can never hurt from a career point of view. After, I am writing this on a Windows Vista powered laptop to see how the other half live as much as anything else.
  11. Domains serviced by hosting resellers can be visible to the systems of those from whom they buy their wholesale hosting. This frustrated my initial attempts to move this blog over because I couldn’t get an account set up for technologytales.com because a reseller had it already on the same system. It was only when I got the reseller to delete the account with them that things began to run more smoothly.
  12. If things are not going as you would like them, getting your account deleted might be easier than you think so don’t procrastinate because you think it a hard thing to do. Of course, it goes without saying that you should back things up beforehand.
Web Development

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java.net.MalformedURLException: unknown protocol: j

December 15, 2007 No comments

I know that that there better things to call a blog post than to use part of an error message that I got from Saxonica‘s Saxon while I was converting XML files into PHP equivalents for the visitor information section of my main website. I use the open source Saxon-B rather than the commercial Saxon-SA and it fulfils all of my needs and version 8 and later (it has now reached 9.0.0.2) handle the XSLT 2.0 features that I need to make the transformations really clever. Also, because Saxon is available as a jar file, it is cross platform so long as you have Java on board. There are, however, some slight differences in behaviour. I now run thte thing in Linux and any Windows-style file locations are not recognised. I had the file path in a DTD declaration starting with "J:\" and that was thought to be a protocol like file, http, https, ftp and so on because of the colon. There’s no j protocol so Java gets confused and, voilà!, you get the rather obscure error that titles this post. Otherwise, the migration of the Perl script that creates XSLT files and fires off the required XML to PHP transformations was a fairly straightforward exercise once file locations and shebang line were set right.

Web Development

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Setting up a test web server on Ubuntu

November 1, 2007 No comments

Installing all of the bits and pieces is painless enough so long as you know what’s what; Synaptic does make it thus. Interestingly, Ubuntu’s default installation is a lightweight affair with the addition of any additional components involving downloading the packages from the web. The whole process is all very well integrated and doesn’t make you sweat every time you to install additional software. In fact, it resolves any dependencies for you so that those packages can be put in place too; it lists them, you select them and Synaptic does the rest.

Returning to the job in hand, my shopping list included Apache, Perl, PHP and MySQL, the usual suspects in other words. Perl was already there as it is on many UNIX systems so installing the appropriate Apache module was all that was needed. PHP needed the base installation as well as the additional Apache module. MySQL needed the full treatment too, though its being split up into different pieces confounded things a little for my tired mind. Then, there were the MySQL modules for PHP to be set in place too.

The addition of Apache preceded all of these but I have left it until now to describe its configuration, something that took longer than for the others; the installation itself was as easy as it was for the others. However, what surprised me were the differences in its configuration set up when compared with Windows. Same software, different operating system and they have set up the configuration files differently. I have no idea why they did this and it makes no sense at all to me; we are only talking about text files after all. The first difference is that the main configuration file is called apache2.conf in Ubuntu rather than httpd.conf as in Windows. Like its Windows counterpart, Ubuntu’s Apache does uses subsidiary configuration files. However, there is an additional layer of configurability added courtesy of a standard feature of UNIX operating systems: symbolic links. Rather than having a single folder with the all configuration files stored therein, there are two pairs of folders, one pair for module configuration and another for site settings: mods-available/mods-enabled and sites-available/sites-enabled, respectively. In each pair, there is a folder with all of the files and another containing symbolic links. It is the presence of a symbolic link for a given configuration file in the latter that activates it. I learned all this when trying to get mod_rewrite going and changing the web server folder from the default to somewhere less susceptible to wrecking during a re-installation or, heaven forbid, a destructive system crash. It’s unusual but it does work, even if it takes that little bit longer to get things sorted out when you first meet up with it.

Apart from the Apache set up and finding the right things to install, getting a test web server up and running was a fairly uneventful process. All’s working well now and I’ll be taking things forward from here; making website Perl scripts compatible with their new world will be one of the next things that need to be done.

Databases, Linux, Operating Systems, Programming, Scripting, Software, Web Development, Web Technologies

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Tidying dynamic URL’s

June 15, 2007 One comment

A few years back, I came across a very nice article discussing how you would make a dynamic URL more palatable to a search engine and I made good use of its content for my online photo gallery. The premise was that URL’s looking like that below are no help to search engines indexing a website. Though this is received wisdom in some quarters, it doesn’t seem to have done much to stall the rise of WordPress as a blogging platform.

http://www.mywebsite.com/serversidescript.php?id=394

That said, WordPress does offer a friendlier URL display option too and you can see this in use on this blog; they look a little like the example URL that you see below and the approach is equally valid for both Perl and PHP. I have using the same approach for the Perl scripts powering my online phone gallery and now want to apply the same thinking to a gallery written in PHP:

http://www.mywebsite.com/serversidescript.pl/id/394

The way that both expressions work is that a web server will chop pieces from a URL until it reaches a physical file. For a query URL, the extra information after the question mark is retained in its QUERY_STRING variable while extraneous directory path information is passed in the variable PATH_INFO. For both Perl and PHP, these are extracted from the entries in an array; for Perl, this array is called is $ENV and $_SERVER is the PHP equivalent. Thus, $ENV{QUERY_STRING} and $_SERVER{‘QUERY_STRING’} traps what comes after the "?" while $ENV{PATH_INFO} and $_SERVER{‘PATH_INFO’} picks up the extra information following the file name (the "/id/394/" in the example). From there on, the usual rules apply regarding cleaning of any input but changing from one to another should be too arduous.

Scripting, Web Development

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