|
The file specified by the EMBPERL_OBJECT_BASE apache directive
(usually called base.epl) is the lynchpin of how EmbperlObject
operates. Whenever a request comes in for any page on this website,
Emperl will look for base.epl - first in the same directory as the
request, and if not found there then working up the directory tree to
the root dir of the website. For example, if a request comes in for
http://www.yoursite.com/foo/bar/file.html, then Embperl first looks
for /foo/bar/base.epl. If it doesn't find base.epl there, then
it looks in /foo/base.epl. If no luck, then finally
/base.epl. (These paths are all relative to the document root for
the website). What is the point of all this? In a nutshell, base.epl is a template for giving a common
look-and-feel to your web pages. This file is what is actually used to
build the response to any request, regardless of the actual filename
which was asked for. So even if file.html was requested,
base.epl is what is actually executed. base.epl is a normal
file containing valid HTML mixed with Perl code, but with a couple of
small differences. Here's a simple 'Hello World' example of this
approach: /base.epl
<HTML>
<HEAD>
<TITLE>Some title</TITLE>
</HEAD>
<BODY>
Joe's Website
<P>
[- Execute ('*') -]
</BODY>
</HTML> /hello.html
Hello world! Now, if the file http://www.yoursite.com/hello.html is requested, then
base.epl is what will actually get executed initially. So where
does the file hello.html get into the picture? Well, the key is the
'*' parameter in the call to Execute(). '*' is a special filename,
only used in base.epl. It means, literally, "the filename which
was actually requested". What you will see if you try this example is something like this: Joe's Website Hello world! As you can see here, the text "Joe's Website" is from base.epl and
the "Hello world!" is from hello.html. This architecture also means that only base.epl has to have the
boilerplate code which every HTML file normally needs to contain -
namely the <HTML> <BODY>, </HTML> and so on. Since the '*' file is
simply inserted into the code, all it needs to contain is the actual
content which is specific to that file. Nothing else is necessary,
because base.epl has all the standard HTML trappings. Of course,
you'll probably have more interesting content, but you get the point.
|
