ch1.htm

美国Macmillan出版社编写的Perl教程《Perl CGI Web Pages for WINNT》

utility awk. Awk is used by UNIX programmers to manipulate structured
data and produce formatted reports. Awk's main power lies behind
the use of regular expressions, a syntax that is common to UNIX
utilities. Regular expressions are a powerful way to manipulate
text, and this power is harnessed by Perl. The gory details about
regular expressions in Perl are dealt with in <A HREF="ch3.htm" tppabs="http://210.32.137.15/ebook/PC%20Magazine%20Programming%20Perl%205.0%20CGI%20Web%20Pages%20for%20Microsoft%20Windows%20NT/ch3.htm" >Chapter 3</A>
<P>
Perl was developed to help UNIX users with tasks that are too
heavy, or too portability-sensitive, for a shell. With UNIX, the
operating system is utilized through a shell, like the Bourne
or Korn shell. The shell provides an interface where the UNIX
user can run applications, rename files, and perform various housekeeping
tasks. This is different from the Windows method of interfacing
that Microsoft has developed, and more like using DOS or MS-DOS.
<P>
In this instance you can compare using a UNIX shell to using MS-DOS.
Both appear on the screen in the form of a text-driven terminal
screen and both operate from the command line. Often software
used by Windows is set up using MS-DOS first to extract and install
the various files involved. The commands available to you in MS-DOS
to perform tasks beyond this are fairly limited. For a larger
job, like automating a login sequence, you have to use a short
program, sometimes called a script.
<P>
Instead of creating an entire specialized program using a high-level
language like C, you might want to write a simple script using
a mid-level, or scripting, language. A simple comparison will
illustrate the difference between the two languages.
<P>
Listing 1.1 is a script in C to replace all the occurrences of
the letter &quot;o&quot; in a string[]:
<HR>
<BLOCKQUOTE>
<B>Listing 1.1 Example of a Script in C<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<PRE>
#include &lt;memory.h&gt;
#include &lt;string.h&gt;
#include &lt;stdio.h&gt;
int  ch = 'o';
int  newch = 'p';
char string[] = &quot;The quick brown dog jumps over the lazy fox&quot;;
void main()
{
    char *pdest;
    int result;
    printf( &quot;String to be searched:\n\t\t%s\n&quot;, string );
    printf( &quot;Search char:\t%c\n&quot;, ch );
    printf( &quot;Replace with char:\t%c\n&quot;, newch );
    pdest = strchr( string, ch );
    while ( pdest != NULL ) 
    {
        result = pdest - string + 1;
        printf( &quot;Result:\t\t%c found at position %d\n\n&quot;, ch, result );
        string[result]=newch;
        pdest = strchr( string, ch );
    }
    printf( &quot;The new String:\n\t\t%s\n&quot;, string );
}
</PRE>
</BLOCKQUOTE>
<HR>
<P>
Listing 1.2 is the comparable script in Perl. It is obvious-even
to the inexperienced programmer-which language is easier to use
when handling text at this level.
<P>
In the UNIX world, Perl was created as just such a language. Its
purpose was to handle these mid-level jobs that would be too much
for the shell, and too little to justify using C.
<P>
This is not to imply that MS-DOS is exactly like a UNIX shell.
There are several major differences between them, the biggest
of which is how they differ in the method by which they handle
the resources available to the computer. This comparison of the
two terminal windows is only meant on the conceptual level, and
using a UNIX shell is very similar in experience to using MS-DOS,
for those of you who have never worked with UNIX.
<HR>
<BLOCKQUOTE>
<B>Listing 1.2 Perl Script<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<PRE>
#!/usr/bin/perl
$string = &quot;The quick brown dog jumps over the lazy fox&quot;;
$ch = 'o';
$newch = 'p';
print &quot;String to be searched:\n\t\t$string\n&quot;;
print &quot;Search Char: $ch\n&quot;;
print &quot;Replace with Char: $newch\n&quot;;
$string =~s/$ch/$newch/g;
print &quot;The new string:\n\t\t$string\n&quot;;
</PRE>
</BLOCKQUOTE>
<HR>
<P>
a UNIX shell is very similar in experience to using MS-DOS, for
those of you who have never worked with UNIX<BR>
<P>
<CENTER>
<TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>
<TR VALIGN=TOP><TD><B>NOTE</B></TD></TR>
<TR VALIGN=TOP><TD>
<BLOCKQUOTE>
<I>A real examination of MS-DOS and UNIX is a little outside the scope of this book, but if you want to learn more about UNIX and UNIX shells, you can try these books published by O'Reilly &amp; Associates, Inc.: </I>
</BLOCKQUOTE>
<BLOCKQUOTE>
<I>Grace Todino, John Stang, and Jerry Peek's Learning the UNIX Operating System </I>
</BLOCKQUOTE>
<BLOCKQUOTE>
<I>Daniel Gilly's UNIX in a Nutshell: System V Edition</I>
</BLOCKQUOTE>
<BLOCKQUOTE>
<I>Bill Rosenblatt's Learning the Korn Shell </I>
</BLOCKQUOTE>
<BLOCKQUOTE>
<I>Dale Dougherty's sed &amp; awk</I>
</BLOCKQUOTE>

</TD></TR>
</TABLE></CENTER>
<P>
<P>
The initial purpose of Perl has grown by leaps and bounds. Now
found among Perl's various applications is the ability for Perl
to act as a CGI language on an Internet or an intranet server
to help provide Web services and systems administration tools.
It is this application of Perl that interests us most in this
book.
<H3><A NAME="TheAdvantagesofPerl">
The Advantages of Perl</A></H3>
<P>
Perl creates a more succinct and clear way of doing many tasks
that C, or one of the UNIX shells, does, but without a lot of
fuss. Unlike a compiled language like C or C++, Perl is an interpreted
script language. One of the things that means is that it has a
much shorter development cycle. 
<P>
Perl is also flexible. It runs on many different server setups
without needing much, if any, reconfiguration. Perl is available
for the Sun OS, AIX, Windows NT (WinPerl), and even Macintosh
platforms.
<P>
Perl, especially where CGI is concerned, is extremely portable.
If you want to use a script on a different operating system, you
just pack up your Perl file and bring it along. Think about Perl
scripts as though they were Lego blocks, and consider how you
can use different blocks that have their own function to build
new structures, then take them apart to build something different.
Not only can you develop Perl libraries to assist you in creating
more complex scripts, but you can also bring your work home with
you. Those of you in the freelance world are quite familiar with
the pressure placed on you to solve problems quickly. Perl lets
you develop a very efficient bag of tricks that you can take from
project to project that will let you spend more of your time solving
the problem instead of hammering out unique scripts each and every
time.
<P>
Perl is a language that is easy to read. The commands in a Perl
script are much more accessible than many other languages, usually
because other older languages have kept archaic and mystical aspects
that just confuse most people.
<P>
Perl is also quite powerful because it combines the versatility
and efficiency of a shell language with the ability to make low-level
system calls that you would expect from a C program. Perl can
work with many different text search tools, such as WAIS or Glimpse,
relational databases, such as Sybase and Oracle, and object-relational
packages like Illustra. This is a point that no Web programmer
should ever forget when dealing with the many different executables
on the market. Though your software ranges in its standards and
preferences, Perl can work with each one of them. Perl functions
on a level below a programmable &quot;layer&quot; between the
user and an information source, like a text file.
<P>
It must be stated though that not all of your CGI problems will
be solved with Perl. Often, a combination of CGI languages is
needed to overcome bug hurdles. There are no hard and fast programming
rules with CGI, so a clear understanding of the client-server
cycle, and its related protocols, should be taken to heart.
<P>
While Perl was originally designed with the UNIX operating system
in mind, there are now several other UNIX-like operating systems
that can handle it, Windows NT being one of them.
<H3><A NAME="LocatingPerl">
Locating Perl</A></H3>
<P>
For being such a relatively new programming language, Perl has
a very active programming community behind it. In fact, it's hard
to find someone who has anything bad to say about this language.
There are many sites on the World Wide Web that have Perl FAQ
lists, archives, and script libraries. Some of the more popular
of these are listed below:
<UL>
<LI><I><A HREF="javascript:if(confirm('http://www.inxpress.net/~moewes/comput  \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address.  \n\nDo you want to open it from the server?'))window.location='http://www.inxpress.net/%7Emoewes/comput'" tppabs="http://www.inxpress.net/%7Emoewes/comput">http://www.inxpress.net/~moewes/comput</A></I>-Perl for Windows
NT
<LI><I><A HREF="javascript:if(confirm('http://www.bhs.com/cgi-shl/dbml.exe?template=/BHS/winnt  \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address.  \n\nDo you want to open it from the server?'))window.location='http://www.bhs.com/cgi-shl/dbml.exe?template=/BHS/winnt'" tppabs="http://www.bhs.com/cgi-shl/dbml.exe?template=/BHS/winnt">http://www.bhs.com/cgi-shl/dbml.exe?template=/BHS/winnt</A></I>-Beverly
Hills Software Windows NT Resource Center
<LI><I><A HREF="javascript:if(confirm('http://www.bio.cam.ac.uk/cgi-lib/  \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address.  \n\nDo you want to open it from the server?'))window.location='http://www.bio.cam.ac.uk/cgi-lib/'" tppabs="http://www.bio.cam.ac.uk/cgi-lib/">http://www.bio.cam.ac.uk/cgi-lib/</A></I>-The cgi-lib.pl Home
Page
<LI><I><A HREF="javascript:if(confirm('http://www.ics.uci.edu/pub/websoft/libwww-perl/archive/  \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address.  \n\nDo you want to open it from the server?'))window.location='http://www.ics.uci.edu/pub/websoft/libwww-perl/archive/'" tppabs="http://www.ics.uci.edu/pub/websoft/libwww-perl/archive/">http://www.ics.uci.edu/pub/websoft/libwww-perl/archive/</A></I>-libwww-perl
Mailing List Archives
<LI><I><A HREF="javascript:if(confirm('http://www.worldwidemart.com/scripts/  \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address.  \n\nDo you want to open it from the server?'))window.location='http://www.worldwidemart.com/scripts/'" tppabs="http://www.worldwidemart.com/scripts/">http://www.worldwidemart.com/scripts/</A></I>-Matt's Script
Archive
<LI><I><A HREF="javascript:if(confirm('http://www.oac.uci.edu/indiv/ehood/perlWWW/  \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address.  \n\nDo you want to open it from the server?'))window.location='http://www.oac.uci.edu/indiv/ehood/perlWWW/'" tppabs="http://www.oac.uci.edu/indiv/ehood/perlWWW/">http://www.oac.uci.edu/indiv/ehood/perlWWW/</A></I>-Another
good Perl archive of Perl scripts relating to the Web
</UL>
<P>
For Windows NT you need to use a version of Perl that has been
ported to the Windows NT environment. You will probably want to
install Perl on any workstations connected to your server locally
(in a LAN or WAN configuration) so that you can utilize Perl on
your own network as well.
<P>
On the Web you can find Perl for Windows NT (and lots of other
NT goodies) at <A HREF="javascript:if(confirm('http://www.perl.hip.com/.  \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address.  \n\nDo you want to open it from the server?'))window.location='http://www.perl.hip.com/.'" tppabs="http://www.perl.hip.com/.">http://www.perl.hip.com/.
</A><P>
This is the primary place to learn about all Windows NT Perl 5.001
concerns. They also house two e-mail lists, revolving around Windows
NT Perl 5.001, that can be subscribed to by going to the above
URL and registering. You can also join by sending an e-mail message