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Tutorial 3 - Web Hit Counter Using an Image Tag
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How Tricky Is This Trick? :
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When I first learned this way of doing things I thought,
"Gosh, that's a tricky thing to do!" You see, by putting
a program name inside the image tag, the server simply
executes that program instead of serving up an image from
off of a static file. The thing is we're not really
interested in the image per se, only the fact that we
can run our program in the course of generating the
image.
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Nonetheless we're going to have to output an image too. Or
else the web page will have a broken link for the image
and that'll look ugly on older browsers. On newer browsers
it'll be fairly inconspicuous, just a 1x1 pixel dot, because
that's how large we're making the image. Of course while
we're in this program outputting the image, we might as
well do our little counting thing :^).
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Modularization and Subroutines :
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There's a mouthful for you. What's it mean? Modularized
programming is a technique where a program is broken up into
small pieces (called modules, duh) which work together to
produce all of the functionality of the complete program,
only we break it up into these smaller pieces.
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Subroutines are a popular way to implement a modular
design. And beginning with this program we are going to
do everything in a modular fashion, so there's a few things
to explain.
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all variables we use from now on will be declared
with the my
Perl operator, which tells Perl that we are setting
up a certain variable of the given name
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we will henceforth issue the Perl compiler directive
use strict; which
will insure that only explicitely declared variables
are used in our programs
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by combining 'use strict' and 'my variables' we will
help prevent confusion, a large part of what a
modularized approach accomplishes, any variable that
isn't declared will fail in the compile phase and
the program will not run until we fix it
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subroutine names, when called from elsewhere will be
prefixed with the &
character so that we know at a glance that
we're referring to a subroutine, while it's not
required, personally I think it's a darn good idea
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So without further adieu, let's look at the program..
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