ch1.htm

《Perl 5 Unreleased》

distributed with CD collections of utilities for UNIX platforms.
(See appendix B, "Perl Module Archives," for information
on Perl archives.)
<H3><A NAME="InterpretedLanguage1">Interpreted Language</A></H3>
<P>
Perl is interpreted. This can be either an advantage or disadvantage,
depending on your needs. For example, Perl has a short development
cycle compared to compiled languages, but it will never execute
as fast as a compiled language. I discuss the disadvantages in
the section called, &quot;What Are the Negatives of Using Perl?,&quot;
but there are some definite advantages.
<P>
One advantage of an interpreted language for tool or application
development is that you can perform incremental, iterative development
and testing without having to go through a create/compile/test/debug/fix
cycle. By eliminating the compile portion of the cycle, interpreted
languages can speed the development cycle drastically. It can
also be helpful if you are evolving your application by implementing
it with minimal capabilities and adding advanced capabilities
later.
<P>
Because it is interpreted and relatively C-like, you can also
use Perl as a <I>prototyping</I> language. This can be especially
useful with complex or technically difficult projects such as
network communication. You can use Perl's shortened development
cycle to evaluate your design and then, once it is proven, rewrite
the code in the language of your choice. By the way, C and C++
are good choices because Perl is a lot like C and supports much
the same functionality.
<H3><A NAME="Practical">Practical</A></H3>
<P>
Perl is written to be practical. This means that it is
<UL>
<LI><FONT COLOR=#000000>Complete</FONT>
<LI><FONT COLOR=#000000>Easy to use</FONT>
<LI><FONT COLOR=#000000>Efficient</FONT>
</UL>
<P>
These design goals mean that Perl programs can generally accomplish
a goal that would otherwise take several other languages, require
complex programming, and take longer to process.
<P>
But for many of us, practicality goes beyond this. It means that
you can get things <I>done</I> in Perl. In fact, there are usually
several ways that Perl can accomplish the same task. It also means
that the programmer can concentrate on getting the task done rather
than dealing with the &quot;beauty&quot; of the language in which
he or she is working.
<H4>Complete</H4>
<P>
As mentioned before, Perl combines some of the best features of
several languages. Here's a list of these languages:<P>
<CENTER>
<TABLE BORDER=1>
<TR VALIGN=TOP><TD WIDTH=109><CENTER><TT><FONT FACE="Courier">grep/awk</FONT></TT></CENTER>
</TD><TD WIDTH=481>General pattern-matching languages for selecting elements from a file.
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=109><CENTER><TT><FONT FACE="Courier">C</FONT></TT></CENTER>
</TD><TD WIDTH=481>A general-purpose compiled programming language. (Perl is written in C.)
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=109><CENTER><TT><FONT FACE="Courier">sh</FONT></TT></CENTER>
</TD><TD WIDTH=481>A control language generally used for running programs and scripts written in other languages.
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=109><CENTER><TT><FONT FACE="Courier">sed</FONT></TT></CENTER>
</TD><TD WIDTH=481>A stream editor for processing text streams (STDIN/STDOUT).
</TD></TR>
</TABLE></CENTER>
<P>
<P>
These languages typically have been the tools used by UNIX administrators
to accomplish tasks. In fact, they are often touted as the reason
that UNIX is an excellent development platform. They are still
excellent tools for the purposes for which they were written.
<P>
However, if you have to deal with several languages, you also
have to deal with <I>learning</I> these languages. For instance,
a task to process a single text file might require the administrator
to write a shell script to run an <TT><FONT FACE="Courier">awk</FONT></TT>
program to select lines that are subsequently processed by <TT><FONT FACE="Courier">sed</FONT></TT>.
<P>
<A HREF="f1-1.gif" tppabs="http://www.mcp.com/815097600/0-672/0-672-30891-6/f1-1.gif" ><B>Figure 1.1:</B> <I>A single Perl script can often do the work of several other utilities.</I></A>
<P>
With Perl, the administrator or developer can accomplish his goals
in a single, easy-to-use language that performs the same tasks
as these languages.
<P>
With version 5.0 of Perl, the language also supports an object-oriented
approach to pro-gramming. This means that packages/modules can
be distributed as objects and used without knowledge of the underlying
code. These packages can also be extended as they can be in other
object-oriented languages. The key is that programmers only use
the object-oriented features of Perl if they need them for the
particular program they are writing.
<H4>Easy to Use</H4>
<P>
Above all, Perl is a language in which you can <I>do</I> things.
There are usually several ways to accomplish the same task. Although
some techniques are more efficient with system resources than
others, users can generally select the technique that is easier
for them to use (and maintain/enhance in the future) and go with
it.
<P>
The ease of use and completeness make Perl appropriate for quick-and-dirty,
one-time utilities as well as structured, complex applications.
<H4>Efficient</H4>
<P>
Perl is a straight-line language, which means that simple programs
do not have to deal with complex formatting or function/procedure
or object/method structures to accomplish their task. As a simple
example, let's pay homage to programming texts (including this
one) with the &quot;Hello World!&quot; program. Here it is in
C:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">void main()<BR>
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;printf(&quot;Hello World!&quot;);<BR>
}</FONT></TT>
</BLOCKQUOTE>
<P>
And here it is in Perl:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">print 'Hello World!'</FONT></TT>
</BLOCKQUOTE>
<P>
Get in, get out, and get the job done.
<H3><A NAME="LanguageCapabilities">Language Capabilities</A></H3>
<P>
Perl is <I>optimized</I> for text processing and, therefore, is
very efficient at many tasks required of system administrators
and application developers. Many of the files used in UNIX systems
administration are plain text files. Selecting records, processing
the selected records, and reporting exceptions are the heart of
many tasks performed in UNIX administration.
<P>
In the current versions of Perl, the language also includes much
additional functionality, making it appropriate for tasks such
as processing socket calls, embedding in programs written in C,
and maintaining POSIX-compliant systems.
<H3><A NAME="IntegrationwithC">Integration with C</A></H3>
<P>
Perl can access C libraries to take advantage of much of the code
written for this popular language. Utilities included with Perl
distributions enable you to convert the headers for these C libraries
into their Perl equivalents.
<P>
Perl 5.0 can be integrated easily into C and C++ applications.
Perl can call or be called by routines written in C or C++. The
Perl interface is through a set of <TT><FONT FACE="Courier">perl_call_*</FONT></TT>
functions. The call to C libraries is through the XS language
interface.
<H3><A NAME="SpecializedExtensionstoPerl">Specialized Extensions
to Perl</A></H3>
<P>
There are many specialized extensions to Perl, primarily for handling
specific databases such as Oracle, Ingres, Informix. These combine
the strengths of the Perl language with the access to the host
database.
<P>
At the time of this writing, <TT><FONT FACE="Courier">ftp.demon.co.uk</FONT></TT>
(<TT><FONT FACE="Courier">158.152.1.69</FONT></TT>) is the official
repository for database <TT><FONT FACE="Courier">&lt;foo&gt;perls</FONT></TT>
(see the following list), which can be found in <TT><FONT FACE="Courier">/pub/perl/db/perl4/</FONT></TT>.
It's mirrored at <TT><FONT FACE="Courier">ftp.cis.ufl.edu</FONT></TT>
(<TT><FONT FACE="Courier">198.17.47.33</FONT></TT>) in <TT><FONT FACE="Courier">/pub/perl/scripts/db/</FONT></TT>.
<P>
<CENTER>
<TABLE BORDER=1>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">btreeperl</FONT></TT>
</TD><TD WIDTH=186>NDBM extensions</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">ctreeperl</FONT></TT>
</TD><TD WIDTH=186>C-Tree extensions</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">duaperl</FONT></TT>
</TD><TD WIDTH=186>X.500 directory user agent</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">ingperl</FONT></TT>
</TD><TD WIDTH=186>Ingres</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">isqlperl</FONT></TT>
</TD><TD WIDTH=186>Informix</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">interperl</FONT></TT>
</TD><TD WIDTH=186>Interbase</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">oraperl</FONT></TT>
</TD><TD WIDTH=186>Oracle 6 and 7</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">pgperl</FONT></TT>
</TD><TD WIDTH=186>Postgres</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">sybperl</FONT></TT>
</TD><TD WIDTH=186>Sybase 4</TD></TR>
<TR VALIGN=TOP><TD WIDTH=151><TT><FONT FACE="Courier">uniperl</FONT></TT>
</TD><TD WIDTH=186>UNIFY 5.0</TD></TR>
</TABLE></CENTER>
<P>
<P>
See appendix B, &quot;Perl Module Archives,&quot; for more information
on these repositories.
<H3><A NAME="SocketCapability">Socket Capability</A></H3>
<P>
Perl has the capability to read/write TCP/IP sockets. This gives
it the capability to communicate with servers of all types that
rely on socket communication. It also enables you to write utility
and &quot;robot&quot; programs in the Perl language. For example,
Perl's socket capability can be used to write a robot program
to automate the checking of a World Wide Web (WWW) site to verify
the validity of links on your Web pages. This can be especially
useful in keeping a site up-to-date, given the volatility of the
Internet in its relative infancy.
<H3><A NAME="PerlIsRelativelyEasytoLearn">Perl Is Relatively Easy
to Learn</A></H3>
<P>
Unlike many programming languages, Perl is designed to be practical
rather than beautiful. By this I mean that Perl was designed from
the start to be easy to use, efficient, and complete rather than
tiny, elegant, and minimal.
<P>
Programming in Perl is relatively easy, especially if you have
experience in C or another C-like language. Like many scripting
languages, Perl reads its programs from the first line to the
last line. It doesn't require complex structures to be able to
create a program. It does, however, support subroutines or functions
and, in version 5.0, can be object oriented.
<H3><A NAME="PerlHasBuiltInDebuggingFacilities">Perl Has Built-In
Debugging Facilities</A></H3>
<P>
The Perl interpreter has a built-in debugger that can help reduce
the time it takes to debug applications. The debugger is activated
through the use of the <TT><FONT FACE="Courier">-d</FONT></TT>
switch on the command line. In addition, the <TT><FONT FACE="Courier">-w</FONT></TT>
switch provides a complete set of warnings that can be invaluable
in debugging Perl scripts.
<H3><A NAME="PerlHelpIsReadilyAvailable">Perl Help Is Readily
Available</A></H3>
<P>
Because Perl is very popular as a scripting language, there is
a lot of help out there. Newsgroup discussions are a good place
to start when you require help on Perl programming. There are
newsgroups devoted entirely to Perl and newsgroups devoted to
Web page creation in which the majority of the discussion is about
Perl. Here are some of them:<P>
<CENTER>
<TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>
<TR VALIGN=TOP><TD WIDTH=244><I>Newsgroup</I></TD><TD WIDTH=346><I>Comment</I>
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=244><TT><FONT FACE="Courier">comp.lang.perl...</FONT></TT>
</TD><TD WIDTH=346>This set of newsgroups covers information about Perl in general. Much of the discussion in the specific groups covers using Perl for utility purposes and also as a CGI scripting language.
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=244><TT><FONT FACE="Courier">comp.lang.perl.announce</FONT></TT>
</TD><TD WIDTH=346>Provides information about new modules for Perl programming.