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Programming, Administration, Performance Tips
Practical
_
perl
mod
Stas Bekman & Eric Cholet
Practical mod_perl
Practical mod_perl
Stas Bekman and Eric Cholet
Beijing
•
Cambridge
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Farnham
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Köln
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Paris
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Sebastopol
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Tokyo
Chapter 6
CHAPTER 6
Coding with mod_perl in Mind
This is the most important chapter of this book. In this chapter, we cover all the
nuances the programmer should know when porting an existing CGI script to work
under mod_perl, or when writing one from scratch.
This chapter’s main goal is to teach the reader how to think in mod_perl. It involves
showing most of the mod_perl peculiarities and possible traps the programmer
might fall into. It also shows you some of the things that are impossible with vanilla
CGI but easily done with mod_perl.
Before You Start to Code
There are three important things you need to know before you start your journey in a
mod_perl world: how to access mod_perl and related documentation, and how to
develop your Perl code when the
strict
and
warnings
modes are enabled.
Accessing Documentation
mod_perl doesn’t tolerate sloppy programming. Although we’re confident that you’re
a talented, meticulously careful programmer whose programs run perfectly every
time, you still might want to tighten up some of your Perl programming practices.
In this chapter, we include discussions that rely on prior knowledge of some areas of
Perl, and we provide short refreshers where necessary. We assume that you can
already program in Perl and that you are comfortable with finding Perl-related infor-
mation in books and Perl documentation. There are many Perl books that you may
find helpful. We list some of these in the reference sections at the end of each chapter.
If you prefer the documentation that comes with Perl, you can use either its online
version (start at
http://www.perldoc.com/
or
http://theoryx5.uwinnipeg.ca/CPAN/perl/)
or the
perldoc
utility, which provides access to the documentation installed on your
system.
217
This is the Title of the Book, eMatter Edition
Copyright © 2003 O’Reilly & Associates, Inc. All rights reserved.
To find out what Perl manpages are available, execute:
panic% perldoc perl
For example, to find what functions Perl has and to learn about their usage, execute:
panic% perldoc perlfunc
To learn the syntax and to find examples of a specific function, use the
-f
flag and the
name of the function. For example, to learn more about
open( )
, execute:
panic% perldoc -f open
The
perldoc
supplied with Perl versions prior to 5.6.0 presents the information in
POD (Plain Old Documentation) format. From 5.6.0 onwards, the documentation is
shown in manpage format.
You may find the
perlfaq
manpages very useful, too. To find all the FAQs (Fre-
quently Asked Questions) about a function, use the
-q
flag. For example, to search
through the FAQs for the
open( )
function, execute:
panic% perldoc -q open
This will show you all the relevant
question
and
answer
sections.
Finally, to learn about
perldoc
itself, refer to the
perldoc
manpage:
panic% perldoc perldoc
The documentation available through
perldoc
provides good information and exam-
ples, and should be able to answer most Perl questions that arise.
Chapter 23 provides more information about mod_perl and related documentation.
The strict Pragma
We’re sure you already do this, but it’s absolutely essential to start all your scripts
and modules with:
use strict;
It’s especially important to have the
strict
pragma enabled under mod_perl. While it’s
not required by the language, its use cannot be too strongly recommended. It will save
you a great deal of time. And, of course, clean scripts will still run under mod_cgi!
In the rare cases where it is necessary, you can turn off the
strict
pragma, or a part
of it, inside a block. For example, if you want to use symbolic references (see the
perlref
manpage) inside a particular block, you can use
no strict 'refs';
, as follows:
use strict;
{
no strict 'refs';
my $var_ref = 'foo';
$$var_ref = 1;
}
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Chapter 6: Coding with mod_perl in Mind
This is the Title of the Book, eMatter Edition
Copyright © 2003 O’Reilly & Associates, Inc. All rights reserved.

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