High-level programming languages

About Perl's Binding Operator

20^th May 2009

While this piece is as much an aide de memoire for myself as anything else, putting it here seems worthwhile if it answers questions for others. The binding operators, =~ or !~, come in handy when you are framing conditional statements in Perl using Regular Expressions, for example, testing whether x =~ /\d+/ or not. The =~ variant is also used for changing strings using the s/[pattern1]/[pattern2]/ regular expression construct (here, s stands for "substitute"). What has brought this to mind is that I wanted to ensure that something was done for strings that did not contain a certain pattern, and that's where the !~ binding operator came in useful; ^~ might have come to mind for some reason, but it wasn't what I needed.

Controlling the post revision feature in WordPress 2.6

21^st July 2008

While this may seem esoteric for some, I like to be in charge of the technology that I use. So, when Automattic included post revision retention to WordPress 2.6, I had my reservations about how much it would clutter my database with things that I didn't need. Thankfully, there is a way to control the feature, but you won't find the option in the administration screens (they seem to view this as an advanced setting and so don't want to be adding clutter to the interface for the sake of something that only a few might ever use); you have to edit wp-config.php yourself to add it. Here are the lines that can be added and the effects that they have:

Code: define('WP_POST_REVISIONS','0');

Effect: turns off post revision retention

Code: define('WP_POST_REVISIONS','-1');

Effect: turns it on (the default setting)

Code: define('WP_POST_REVISIONS','2');

Effect: only retains two previous versions of a post (the number can be whatever you want, so long as it's an integer with a value more than zero).

Update (2008-07-23):

There is now a plugin from Dion Hulse that does the above for you and more.

java.net.MalformedURLException: unknown protocol: j

15^th December 2007

While I know that there are better things to call a blog post than to use part of an error message that I got from Saxonica's Saxon when I was converting XML files into PHP equivalents for the visitor information section of my main website, it is handy for anyone else needing to look up a solution when they encounter it. In my case, I use the open source Saxon-B rather than the commercial Saxon-SA, and it fulfils all of my needs. 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. Now, I run the thing on Linux, where any Windows-style file locations are not recognised. When I had the file path in a DTD declaration starting with J:\, that was thought to be a protocol like file, http, https, ftp and so on because of the colon. Since there's no j protocol, Java gets confused, issuing 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.

Append or update?

25^th November 2007

SAS can generate many types of output: plain text, XML, PDF, RTF, Excel, etc. With all of these and the SAS procedures like PROC REPORT, PROC TABULATE and so on, it might seem surprising for me to say that I have been generating output with data step PUT and FILE statements. There was, of course, a reason for this: creating text files for loading into a new database-driven software application. At one stage, I also did some data interleaving at the output stage and that's when I discovered that the default behaviour for SAS FILE statements is to completely overwrite a file unless the MOD option was specified. Adding that switches on APPEND behaviour. The code below adds a header in one step, while adding data below it in another. While I know that there are better ways to achieve this, like setting up your data as you want it or using _N_ to ensure that something only appears once, here's another way. As per the Perl, there's often more than one way to do something with SAS.

data _null_;
    file ds_data;
    put "fieldtype;datasetname;datasetlabel;datasetlayout;datasetclass;datasetstandardversion";
run;

data _null_;
    set ds_ispec;
    file ds_data mod;
    line="datasetstandard;"||trim(memname)||";"||trim(memlabel)||";;;"||trim(memver);
    put line;
run;

Setting up a test web server on Ubuntu

1^st November 2007

Installing all 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 need 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. There are times when we get the same software but on different operating systems, which means that configuration files get set up differently. The first difference is that the main configuration file is called apache2.conf on Ubuntu rather than httpd.conf as on Windows. Like its Windows counterpart, Ubuntu's Apache does use 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 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.

Numeric for loops in Korn shell scripting: from ksh88 to ksh93

18^th October 2007

The time-honoured syntax for a for loop in a UNIX script is what you see below, and that is what works with the default shell in Sun's Solaris UNIX operating system, ksh88.

for i in 1 2 3 4 5 6 7 8 9 10
do
    if [[ -d dir$i ]]
    then
        :
    else
        mkdir dir$i
    fi
done

However, there is a much nicer syntax supported since the advent of ksh93. It follows C language conventions found in all sorts of places like Java, Perl, PHP and so on. Here is an example:

for (( i=1; i<11; i++ ))
do
    if [[ -d dir$i ]]
    then
        :
    else
        mkdir dir$i
    fi
done

Perl vs. PHP: A Personal Experience

11^th June 2007

Ever since I converted it from a client-side JavaScript-powered affair, my online photo gallery has been written in Perl. There have been some challenges along the way, figuring out how to use hash tables has been one, but everything has worked as expected. However, I am now wondering if it is better to write things in PHP for the sake of consistency with the rest of the website. I had a go a rewriting the random photo page and, unless I have been missing something in the Perl world, things do seem more succinct with PHP. For instance, actions that formerly involved several lines of code can now be achieved in one. Reading the contents of a file into an array and stripping HTML/XML tags from a string fall into this category, and seeing the number of lines of code halving is a striking observation. I am not going to completely abandon Perl, it's a very nice language, but I do rather suspect that there is now an increased chance of my having a website whose server-side processing needs are served entirely by PHP.

Getting one’s HTTP headers in a twist

9^th June 2007

I am in the process of further linking the content of hillwalking blog into the fabric of other parts of my website. To date, this has included adding a list of all the posts to the site map and a dossier of the latest entries to the site's welcome page. One thing that started to crop up were a series of warnings of the form:

Cannot modify header information - headers already sent by...

The cause of this was my calling a PHP script that was part of my hillwalking blog installation, and this caused Bad Behaviour to be invoked. The result was that an HTTP header was being sent to create a cookie after one already had been sent to display a web page. A spot of conditional coding and the use of an extra flag resolved the problem.

Apparently, there is another surefire way of getting the same result: whitespace before or after the <?php ... ?> tag in an included script. The cookie issue is one that I can understand, but it does seem strange that an attempt is made to send HTTP header information when the latter arises. It causes loads of questions, though...

Restrictions on SAS libraries when macro catalogs are used

8^th June 2007

When you open up a SAS macro catalogue so that its entries for use by other programs, it has a major impact on the ability to change the library reference used to access the catalogue after it has apparently been unlocked.

options mstored sasmstore=bld_v001;

Using the line above will open the catalogue for reading, but there is no way to close it to change the library reference or unassign it until the SAS session is shut down. Even this line will not do the trick:

options nomstored sasmstore='';

What it means in practice is that if you have a standard macro setting up access to a number of standard macro libraries, then that setup macro needs to check for any library references used and not try to reassign them, causing errors in the process.

A web development toolbox

23^rd March 2007

Having been on a web-building journey from Geocities to having a website with my own domain hosted by Fasthosts, it should come as no surprise that I have encountered a number of tools and technologies over this time and that my choices and knowledge have evolved too. I’ll muse over the technologies first before going on to the tools that I use.

Technologies

XHTML

When I started building websites, it was not after HTML 4 got released, and I devoured most if not all of Elizabeth Castro’s Peachpit Visual Quickstart guide to the language within a weekend. Having previously used fairly primitive WYSIWYG tools like Netscape Composer and Claris Home Page, it was an empowering experience and the first edition (it is now on its third) of Jennifer Niederst Robbins’ Web Design in a Nutshell took things much further, becoming something of a bible for a number of years.

When it first appeared, XHTML 1.0 wasn’t a major change from HTML 4, but its stricter more XML-compliant syntax was meant to point the way to the future and semantic markup was at its heart at least as much as it was for HTML 4. XHTML 2.0 is on the horizon and after the modular approach of XHTML 1.1 (which I have never used), it will be interesting to see how it develops. Nevertheless, there is a surprising development in that some people are musing over the idea of having an HTML 5. Let’s hope that the (X)HTML apple cart doesn’t get completely overturned after some years of relative stability. I still bear scars from the browser wars raging in the 1990’s and don’t want to see standards wars supplanting the relative peace that we have now. That said, I don’t mind peaceful progression.

CSS

Only seems to be coming into its own in the last few years and is truly a remarkable technology despite the hobbles that MSIE places on our ambitions. CSS Zen Garden has been a major source of ideas; I wouldn’t have been able to customise this blog as much as I have without them. I was an early adopter of the technology and got burnt by inconsistent browser support; Netscape 4 was the proverbial bête noir back then, fulfilling the role that MSIE plays today. In those days, it was the idea of controlling text display and element backgrounds from a single place that appealed. Since then, I have progressed to using CSS to replace table-based layouts and to control element positioning. It can do more…

JavaScript

Having had a JavaScript-powered photo gallery before my current Perl-driven one, I can say that I have definitely sampled this ever-pervasive scripting language. Being a client-side language rather than a server-side one, it does place you rather at the mercy of the browser purveyors, and it never ceases to amaze me that there is a buzz around AJAX because of this. In fact, the abundance of AJAX cross-browser function libraries is testimony to the need for browser-specific code. Despite my preferences for server-side scripting, I still find a use for JavaScript, and its main use for me these days is to dynamically control CSS elements to do such things as control the height of a page element or whether it is shown or not. Apparently, CSS may get some dynamic capabilities in the future and reduce my dependence on JavaScript. Meanwhile, Jeremy Keith’s DOM Scripting (Friends of Ed) will prove as much of an asset as it has done.

XML

These days, a lot of the raw data underlying my personal website is stored in XML. I did try to dynamically transform the display of the XML into something meaningful with CSS and XSLT when I first scaled its dizzy heights, but I soon resorted to other techniques. Browser support and the complexity of what I required were the major contributors to this. The new strategy involved two different approaches. The first was to create PHP/XHTML pages from the precursor XML offline, and this is how I generate the website’s directory pages. The other one is to process the XML as text to dynamically supply an XHTML page as the user visits it; this is the way that the photo gallery works.

Perl

This still powers all of my photo gallery. While thoughts of changing it all to PHP linger, there is a certain something about the Perl language that keeps it there. I suppose it is that PHP is entangled in the HTML while Perl encases the whole business, and I am reasonably familiar with its syntax these days, which is why it still does a lot of the data processing grunt work that I need.

PHP

PHP is everywhere these days, though it doesn’t attract quite the level of hype that used to be the case. It still appears with its sidekick MySQL in many website applications. Blogging software such as WordPress and content management systems like Drupal, Mambo and Joomla! wouldn’t exist without the pair. It appears on my website as the glue that holds my visitor directories together and is the processing engine of my WordPress blog. And if I ever get to a Drupal element to the site, by no means a foregone conclusion though I am spending a lot of time with it at this time, PHP will continue its presence in my website scripting as it powers that too.

Applications

Macromedia HomeSite

I have a liking for hand coding, so this does most of what I need. When Macromedia (itself since taken over by Adobe, of course) took over Allaire, HomeSite sadly lost its WYSIWYG capability, but the application still soldiers on even though Dreamweaver offers a lot to code cutters these days. Nevertheless, it does have certain advantages over Dreamweaver: it is a fleeter beast to start up and colour codes Perl syntax.

Macromedia Dreamweaver

There was a time when Dreamweaver was solely a tool for visual web page development, but the advent of Dreamweaver UltraDev added server-side development capabilities to the Dreamweaver family. These days, there is only one Dreamweaver version, but UltraDev’s capabilities still live on in the latest version and I would not be surprised if they were taken further in these database-driven times.

Nowadays, Dreamweaver isn’t an application where I spend a great deal of time. In former times, when my site was made up of static HTML pages, I used Dreamweaver a lot, even if its rendering capabilities were a step behind the then-current browser versions. I suppose that it didn’t fit the way in which I worked, but its template-driven workflow would have been a boon back then.

However, my move from a static site to a dynamic one, starting with my photo gallery, has meant that I haven’t used it as much since then. However, with my use of PHP/MySQL components on my site. Its server-side abilities could get the level of investigation that its PHP/MySQL capabilities allow.

Altova XMLSpy Professional

Adding MySQL databases to my web hosting costs money, not a lot, but it could be spent on other (more important?) things. Hence, I use XML as the data store for my photo gallery and XML files are pre-processed into XHTML/PHP pages for my visitor directories before uploading onto the server.

I use XMLSpy to edit and manage the XML files that I use: its ability to view XML in grid format is a killer feature as far as I am concerned and XML validation also proves very useful; particularly when it comes to ensuring that DTD’s and XML files are in step and for the correct coding of XSLT files. There are other features that I need to explore and that would also take my knowledge of the XML further to boot, not at all a bad thing.

Saxon

For processing XML into another file format such as XHTML, you need a parser and I use the free version of Saxon to do the needful, Saxonica offers commercial versions of it. There is, I believe, a parser in XMLSpy, but I don’t use it because Saxon’s command line interface fits better into my workflow. This is a Perl-driven process where XML files are read and XSLT files, one per XML file, are built before both are fed to Saxon for transforming into XHTML/PHP files. It all works smoothly and updating the XML inputs is all that is required.

AceFTP

If I were looking for an FTP client now, it would be FileZilla, but AceFTP has served me well over the last few years, and it looks as if that will continue. It does have some extra features over FileZilla: transfers between remote sites, and scheduling, for example. I have yet to use either, but they look valuable.

Hutmil

In bygone days when I had loads of static HTML files, making changes was a bit of a chore if they affected every single file. An example is changing the year on the copyright message on the page footers. Hutmil, which I found on a magazine cover-mounted disc, was a great time saver in those days. Today, I achieve this by putting this information into a single file and getting Perl or PHP to import that when building the page. The same “define once, use anywhere” approach underlies CSS as well, and scripting very usefully allows you to take that into the XHTML domain.

Apache

Apache is ubiquitous these days, and both the online and offline versions of my site are powered by it. It does require some configuration, but it is a powerful piece of kit. The introduction of 2.2.x meant a big change in the way that configuration files were modularised and while most things were contained in a single file for 2.0.x, the settings are broken up into different files in 2.2.x, and it can take a while to find things again. Without having it on my home PC, I would not be able to use Perl, PHP or MySQL. Apart from this, I especially like its virtual site capability; very useful for offline development.

WordPress

My hosting supplier offers blogs on Blogware, but that didn’t offer the level of configuration that I would have liked. It is true that this is probably true of any host of blogs. I can’t speak for Blogger, but WordPress.com does have its restrictions too. To make my hillwalking blog fit in with the appearance of my photo gallery, I went popped over to WordPress.org to download WordPress so that I could host a blog myself and have maximum control over its appearance. WordPress supports themes, so I created my own and got my blog pages looking as if they are part of my website, rather than looking like something that was bolted on. Now that I think of it, what about WordPress supporting user-created themes? I support that there is the worry of insecure PHP code but what about it?

MySQL

I am between minds on whether this is a technology or a tool. SQL certainly would be a technology standard, but I am not so clear on what MySQL would be. In any case, I have classed it as a tool, and a very useful one at that. It is the linchpin for my WordPress blogs and, if I go for a content management system like Drupal, its role would surely grow. While I do have a lot of experience with using SAS SQL and this helps me to deal with other varieties, there is still a learning curve with MySQL that gets me heading for a good book and Kofler’s The Definitive Guide to MySQL5 (Apress) seems to perform more than adequately in this endeavour.

Paint Shop Pro

As someone who hosts an online photo gallery, it won’t come as a surprise that I have had exposure to image editors. Despite various other flirtations, Paint Shop Pro has been my tool of choice over the years, but it is now set to be usurped by a member of Adobe’s Photoshop family. Paint Shop Pro does have books devoted to it, but it appears that Photoshop gets better coverage and I feel that my image processing needs to be taken up a gear, hence the potential move to Photoshop

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