Tutorial Machine

Perl 101 (Part 5) – Sub-zero Code

The Machine — Tue, 09 Mar 2010 20:24:08 +0000

Well, a very wise man once said that a little knowledge was a dangerous thing…and so, as your Perl scripts become more and more complex, you’re going to bump your head against the principles of software design, and begin looking for a more efficient way of structuring your Perl programs….

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Common Server Errors & Messages

The Machine — Tue, 09 Mar 2010 20:22:26 +0000

I find it seriously frustrating when servers return cryptic error pages. If you’ve ever seen a 403, 404 or 500 message, you know what I mean. Well sort of, maybe… What you might not know is that all these messages, and more are called Server Response Codes. Whenever you contact the server and request a page or execute a CGI script (through your browser), a server will process this request and respond with these codes, that signal certain things: …

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Common Beginners Mistakes

The Machine — Tue, 09 Mar 2010 20:19:55 +0000

Admittedly, even an intermediate level Perl “programmer” (the not-so-Perl-newbie-ish category of people) will make lots of little errors that will give you server errors. Most of them are syntax errors but if youv’e just finished writing 1000+ lines of code, you really don’t want to have to go over every line again because of a syntax error. Some of the most common ones made are listed below – and these are really the killers to watch out for:

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User Info

The Machine — Tue, 09 Mar 2010 20:17:16 +0000

The primary source of information about a user comes from the environment. The HTTP server sets up certain environment variables to contain information about the remote user. In Perl, these variables are accessible through the %ENV associative array. In C, you will need to use the getenv call to access the values of the variables. The relevant variables are:…

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Debugging CGI Scripts

The Machine — Tue, 09 Mar 2010 20:16:10 +0000

This note describes possible causes for errors in CGI scripts, particularly those that lead to a ‘Server 500 Error’ and a terse and unhelpful message advising you to contact the server administrator…

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CGI Environmental Variables

The Machine — Tue, 09 Mar 2010 20:14:33 +0000

One of the methods that the web server uses to pass information to a cgi script is through environmental variables. These are created and assigned appropriate values within the environment that the server spawns for the cgi script. They can be accessed as any other environmental variable, like with getenv() (in C) or %ENV{'VARIABLE_NAME'} (in Perl). Many of them, contain important information, that most cgi programs need to take into account….

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Printing All CGI Environment Variables

The Machine — Tue, 09 Mar 2010 20:12:16 +0000

The best way to learn about this program is to look at the source code and the output it produces. Therefore, with no further ado, Listing 1 contains the entire source code for this little CGI program:…

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Sorting Techniques

The Machine — Tue, 09 Mar 2010 20:10:48 +0000

Now the first five rows should be ok, they’re just like math. But what are the <=> and cmp operators? Basically, the expression $a <=> $b (or $a cmp $b for strings) returns one of the values 1, 0, -1 if $a is, respectively, larger, equal or lower than $b. (see table below)…

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Untangling Lists & Hashes

The Machine — Tue, 09 Mar 2010 20:09:31 +0000

If you want to blow your mind — in the totally legal sense — spend some time working with Perl’s list and hash data structures. As a means to organize, structure, and manipulate data both lists and hashes are remarkably useful and versatile…

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Benchmarking Perl

The Machine — Tue, 09 Mar 2010 20:08:18 +0000

Perl’s Benchmark module is an extremely useful tool for measuring the speed of your scripts, whether in their entirety, or down to the level of particular subroutines, or single lines of code. While some may want to comb over a script to optimize the speed of every expression, benchmarking is also incredibly helpful in finding significant bottlenecks in a script — segments of code that eat up the majority of processing time. Often, focusing on optimizing one or two main bottlenecks can improve an entire script’s execution time dramatically….

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