Practical mod_perl, from O'Reilly. | 11
By Stas Bekman and Eric Cholet
O'Reilly & Associates, May 2003
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
warnings modes are enabled.
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 information 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.
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 (Frequently 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 examples, 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:
It's especially important to have the
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';
my $var_ref = 'foo';
$$var_ref = 1;
Starting the block with
no strict 'refs';
allows you to use symbolic references in the rest of the block. Outside this
block, the use of symbolic references will trigger a runtime error.
Created: March 27, 2003
Revised: July 23, 2003