Apache: The Definitive Guide, 3rd Edition

Perl

You can download Perl for free from http://www.perl.org. Read the README and INSTALL files and do what they say. Once it is installed on a Unix system, you have an online manual. perldoc perldoc explains how the manual system works. perldoc -f print, for example, explains how the function print works; perldoc -q print finds “print” in the Perl FAQ.

A simple Perl script looks like this:

#! /usr/local/bin/perl -wT
use strict;

print "Hello world\n";

The first line, the “shebang” line, loads the Perl interpreter (which might also be in /usr/bin/perl) with the -wT flag, which invokes warnings and checks incoming data for “taint.” Tainted data could have come from Bad Guys and contain malicious program in disguise. -T makes sure you have always processed everything that comes from “outside” before you use it in any potentially dangerous functions. For a fuller explanation of a complicated subject, see Programming Perl by Larry Wall, Jon Orwant, and Tom Christiansen (O’Reilly, 2000). There isn’t any input here, so -T is not necessary, but it’s a good habit to get into.

The second line loads the strict pragma: it imposes a discipline on your code that is essential if you are to write scripts for the Web. The third line prints “Hello world” to the screen.

Having written this, saved it as hello.pl and made it executable with chmod +x hello.pl, you can run it by typing ./hello.pl.

Whenever you write a new script or alter an old one, you should always run it from the command line first to ...