A BRIEF STUDY OF
PERL
Table of Contents
1. Introduction
INTRODUCTION
What is Perl?
Perl is a programming language which can be used for a large
variety of tasks. A typical simple use of Perl would be for
extracting information from a text file and printing out a report
or for converting a text file into another form. But Perl provides
a large number of tools for quite complicated problems, including
systems programming.
Programs written in Perl are calledPerl scripts, whereas the
termthe perl programrefers to the system program named perl for
executing Perl scripts. (What, confused already?)
If you have used shell scripts orawkorsedor similar (Unix)
utilities for various purposes, you will find that you can normally
use Perl for those and many other purposes, and the code tends to
be more compact. And if you haven't used such utilities but have
started thinking you might have need for them, then perhaps what
you really need to learn is Perl instead of all kinds of
futilities.
Perl is implemented as an interpreted (not compiled) language.
Thus, the execution of a Perl script tends to use more CPU time
than a corresponding C program, for instance. On the other hand,
computers tend to get faster and faster, and writing something in
Perl instead of C tends to saveyourtime.
Origin of language :
Perl began as the result of one man's frustration and, by his
own account, inordinate laziness. It is a unique language in ways
that cannot be conveyed simply by describing the technical details
of the language. Perl is a state of mind as much as a language
grammar.
One of the oddities of the language is that its name has been
given quite a few definitions. Originally, Perl meant the Practical
Extraction Report Language. However, programmers also refer to is
as the Pathologically Eclectic Rubbish Lister. Or even, Practically
Everything Really Likable.
Back in 1986, Larry Wall found himself working on a task which
involved generating reports from a lot of text files with cross
references. Being a UNIX programmer, and because the problem
involved manipulating the contents of text files, he started to use
awk for the task. But it soon became clear that awk wasn't up to
the job; with no other obvious candidate for the job, he'd just
have to write some code.
Larry could have just written a utility to manage the particular
job at hand and gotten on with his life. He could see, though, that
it wouldn't be long before he'd have to write another special
utility to handle something else which the standard tools couldn't
quite hack. (It's possible that he realized that most programmers
werealwayswriting special utilities to handle things which the
standard tools couldn't quite hack.)
So rather than waste any more of his time, he invented a new
language and wrote an interpreter for it. If that seems like a
paradox, it isn't really-it's always a bit more of an effort to set
yourself up with the right tools, but if you do it right, the
effort pays off.
Similar to C ?
Perl programs bear a passing resemblance to C programs, perhaps
because Perl was written in C, or perhaps because Larry found some
of its syntactic conventions handy. But Perl is less pedantic and a
lot more concise than C.
Perl can handle low-level tasks quite well, particularly since
Perl 5, when the whole messy business of references was put on a
sound footing. In this sense, it has a lot in common with C. But
Perl handles the internals of data types, memory allocation, and
such automatically and seamlessly.
This habit of picking up interesting features as it went
along-regular expressions here, database handling there-has been
regularized in Perl 5. It is now fairly easy to add your favorite
bag of tricks to Perl by using modules. It is likely that many of
the added-on features of Perl such as socket handling will be
dropped from the core of Perl and moved out to modules after a
time
Cost and Licensing :
Perl is free. The full source code and documentation are free to
copy, compile, print, and give away. Any programs you write in Perl
are yours to do with as you please; there are no royalties to pay
and no restrictions on distributing them as far as Perl is
concerned.
It's not completely "public domain," though, and for very good
reason. If the source were completely public domain, it would be
possible for someone to make minor alterations to it, compile it,
and sell it-in other words, to rip off its creator. On the other
hand, without distributing the source code, it's hard to make sure
that everyone who wants to can use it.
The GNU General Public License is one way to distribute free
software without the danger of someone taking advantage of you.
Under this type of license, source code may be distributed freely
and used by anybody, but any programs derived using such code must
be released under the same type of license. In other words, if you
derive any of your source code from GNU-licensed source code, you
have to release your source code to anyone who wants it. Perl is
released under the terms of the "Artistic" license. This is a
variation on the GNU General Public License which says that anyone
who releases a package derived from Perl must make it clear that
the package is not actually Perl. All modifications must be clearly
flagged, executables renamed if necessary, and the original modules
distributed along with the modified versions. The effect is that
the original author is clearly recognized as the "owner" of the
package. The general terms of the GNU General Public License also
apply.
Installing Perl :
It's critically important to have Perl installed on your
computer before reading too much further. As you read the examples,
you'll want to try them. If Perl is not already installed, momentum
and time will be lost.
It is very easy to see if your system already has Perl
installed. Simply go to a command-line prompt and type:
perl -v
Hopefully, the response will be similar to this:
This is perl, version 5.001
Unofficial patchlevel 1m.
Copyright 1987-1994, Larry Wall
Win32 port Copyright 1995 Microsoft Corporation. All rights
reserved.
Developed by hip communications inc.,
http://info.hip.com/info/
Perl for Win32 Build 107
Built Apr 16 1996@14:47:22
Perl may be copied only under the terms of either the Artistic
License or the GNU General Public License, which may be found in
the Perl 5.0 source kit.
If you get an error message or you have version 4 of Perl,
please see your system administrator or install Perl yourself. The
next section describes how to get and install Perl.
For UNIX and OS/2
-- The Perl Home Page contains a software link
(http://www.perl.com/perl/info/software.html) that will enable you
to download the latest Perl source code. The page also explains why
Perl binaries are not available. Hopefully, your system will
already have Perl installed. If not, try to get your system
administrator to install it.
For Windows 95/Windows NT
-The home page of hip communications, inc.
(http://www.perl.hip.com) contains a link to download thei86
Release Binary. This link lets you download a zip file that
contains the Perl files in compressed form. CD-ROM copiess are
freely distributed with many Perl books and also on CDROM: for
example,Perl - Walnut Greek CD-ROM
For Macintosh Computers
--MacPerlis a ported version of Perl with a basic but very
useable User Interface.It is available from
http://www.iis.ee.ethz.ch/neeri/macintosh/perlman/perl_toc.html,
http://www.unimelb.edu.au/ssilcot/macperl-primer/.
It also comes on CD-ROM with many Perl Books
Recommended Reading
Teach Yourself Web Publishing with HTML 3.2 in 14 Days,Laura
Lemay, Sams.Net Publishing.
The Internet Unleashed,J. Ellsworth, B. Baron, et al., Sams.Net
Publishing
The Internet Complete Reference(2nd Ed.),H. Hahn,
McGraw-Hill
Webmaster in a Nutshell,S. Spainhour and V. Quercia, O'Reilly
and Associates Inc.
Every Student's Guide to the World Wide Web,K. Pitter and R.
Minato, McGraw Hill
HTML Sourcebook,I.S. Graham, Wiley and Sons
HTML: The Definitive Guide,C. Musciano and B. Kennedy, O'Reilly
and Associates Inc.
