TweetFollow Us on Twitter

Introduction to Perl for Mac OS X

Volume Number: 18 (2002)
Issue Number: 9
Column Tag: Mac OS X

Introduction to Perl for Mac OS X

There's more than one way to do it.

by Joe Zobkiw

What is Perl?

Perl is short for "Practical Extraction and Report Language." However, Perl really doesn't sound too interesting when you put it in those terms, so, now that you know that much, forget everything that you've learned up to this point.

Perl is an advanced, cross-platform programming language created by Larry Wall. It's strength lies in the fact that it can perform extremely complex tasks easily while not being too big or bulky for the simpler tasks. It is an expert at manipulating text, strings, numbers, streams of data, files and directories. It can just as easily massage massive amounts of data on your local computer as it can connect to a remote server, across an ocean, and feed it in streams. As long as you don't need a fancy GUI, Perl may just have an answer for you. In a word, Perl is elegant.

Perl and Mac OS X

Perl (verion 5.6 as of this writing) comes pre-installed with Mac OS X so there really isn't anything to install or configure. You can create a Perl script with any text editor. I use BBEdit from Bare Bones Software since it automatically colors the syntax of your Perl script and is simply the best programmer's text editor available for Mac OS X. Because Perl is based in the command line, you primarily run Perl scripts using the Terminal application that comes with Mac OS X. Don't let this scare you though, as you'll soon learn, the Terminal isn't so scary.


Figure 1. Perl running in Terminal.

As you can see in Figure 1, we ran Perl from within the Terminal passing the -v command. This tells Perl to spit back its version information. In this example we are using Perl 5.6.0 specifically built for Mac OS X. We then called Perl passing the -e command which tells Perl that we are including actual Perl code between the single quotes and expect it to be interpreted, executed and the results displayed in the Terminal. Perl performed the task flawlessly, as it told us Hello!

Most of the time you will write your Perl scripts and store them in a text file. These files end in .pl and should be saved with UNIX linefeeds, otherwise Perl will get confused and return confusing errors when it attempts to run your scripts. Remember, with Mac OS X you are really running the UNIX operating system underneath a Macintosh user experience! Assume we have the following text stored in a file named myfirstscript.pl:

#!/usr/bin/perl
print "Hello from Perl on Mac OS X!\n";

Note that that the very first line of the script points to Perl. This is how all Perl scripts must start - with the path to Perl. The line may be slightly different depending on your operating system but this is what you will usually see with Mac OS X. The # symbol is actually a comment designator. Normally whenever you see this symbol, anything to the right of it is a comment. The next line gives Perl the command to print to the Terminal. Looks just like what we typed on the command line earlier! To run this script using Terminal you first open Terminal, use the cd command to point to the directory which contains the script and then type perl myfirstscript.pl. Upon pressing return your script will execute and you'll see the "hello..." message printed on the screen! Now all that's left to do is write a script that actually does something.

One thing to remember is that Perl is a complex programming language that entire books were written about. It is impossible to go into all of the intricacies of the language in this short article. As you continue to read you will learn some of the basics and some great places to turn to learn the language itself. So don't turn away just yet...half a million programmers can't be wrong!

So What Can I Do With Perl?

Now that you know the basics of how Perl fits into Mac OS X and how you create and execute scripts, what is it actually good for?

Let's say you have a bunch of ASCII text files that you need to scan for certain characters, change them to something else, then make a copy of the altered file and the original. If this was a one-time occurrence you might just spend 5 hours and do it by hand. However, if this is part of a process that you have to perform every day or even every month, why not the let the computer - with the help of Perl - do it for you? You could literally write such a program in Perl in less than 20 lines of code. Adding a few more lines of code would be all you would need to make it email or page you when it was finished processing. I know people in the corporate world who have their entire jobs automated - they can start a process and go biking for the rest of the day - if there is a problem (or upon success) their Perl scripts page them!

As you may already know most everything you send or receive via the Internet is text-based. The HTTP protocol that web servers use is a completely text-based protocol. Your web browser sends a text request to the server, which sends a text response in return. Your e-mail program works the same way. News readers work the same way. As do many of the simpler, more behind-the-scenes protocols such as Ping, Telnet and Finger.

Given this, you can relatively easily write an anti-spam Perl script that logs into your email server and deletes any email that contains the words "GET RICH" in the subject - before you ever get a chance to see them. How about a script that pulls down the latest weather information from a web site and emails you when an advisory is posted for your area. Consider a script that watches a newsgroup for job postings of interest and automatically emails them to you. The possibilities are literally endless when you look at all the data available on the net!

I recently wrote a Perl script that reads data from a GPS that is connected via a Keyspan USB PDA adapter locally to my computer. The script (available online at http://homepage.mac.com/zobkiw/) opens the Keyspan driver and begins reading and parsing position data being sent by the GPS. Once parsed, I can easily display detailed, self-updating maps (read from the Internet) showing my position. Given this technique, you can hook up any RS232-type device to your Mac and communicate with it via Perl. This would include personal weather stations, amateur radios, musical instruments, custom hardware and many other little gadgets.

A More Advanced Example

Now that you have an idea of some of the things you can do with Perl, let's specifically take a look at a more advanced example. The example that we will walk through pulls the current page displayed at cnn.com (although you can easily change it to support any web site) and reports if certain words are "in the news." Take a look at the code and then we will explain it in detail.

#!/usr/bin/perl
use strict;
my @a = ("Clinton", "Gore", "Bush", "Cheney");
my $url = "http://www.cnn.com";
my $sysstring = "curl -s $url";
my $count = 1;
print "Opening...\n";
open(FOO, "$sysstring|");
print "Searching...\n";
while (<FOO>){
   my $lineout = $_;
   foreach my $search (@a) {
      if ($lineout =~ /$search/){
         print "$count. $search found.\n";
         $count++;
      }
   }
}
close FOO;
print "Complete.\n";

This is a pretty good example of Perl performing a complex task - easily. If you think about what is going on here in detail: your computer has to use DNS to resolve the cnn.com web site name to the proper IP address; connect to it; create the proper http request to obtain the contents of the web page; then search the web page for particular text and display the results. If you were to write this code by hand, following the multiple protocols (DNS and http), it might take you days - if not longer. Let's look at the code!

We've already discussed the very first line, which points to Perl itself so we will begin with use strict. The Perl keyword use is used like the keyword include in C. Whenever you need to let Perl know you will be making use of a module, or in this case, the services of Perl itself, you use the word use. Specifically, use strict tells Perl that you want it to be a bit stricter than it would otherwise be as it interprets your code. In Perl, there are more ways to perform a task than in C - hence the Perl motto "There's more than on way to do it.". It is very easy to make a mistake. Enabling strict helps to catch common problems before they cause you to lose your hair.

The next four lines declare some variables. The Perl keyword my is used to explicitly declare variables. In reality you don't have to declare variables in Perl, it will automatically create any variable you attempt to use. However, remember use strict. One of the features of strict is that Perl requires us to employ my to declare the variables we use before we use them. This can help with the hair loss mentioned earlier.

The first variable, a, is an array of strings. We use the @ symbol to signify an array of items. The items in the array follow in parenthesis and quotes. $url is a variable named url. Most variable names in Perl begin with a $. I say most because although a is a variable, it is also an array, so it starts with an @ symbol. It may seem confusing now but as you work with Perl you will begin to appreciate the power that Perl offers as it confuses you.

$sysstring is a variable that contains a command line command. The curl program is one that you can execute from the command line, that is, the Terminal. Curl is a client program that retrieves data from (and sends data to) various servers. It supports numerous protocols including http, https, FTP, GOPHER, DICT, TELNET, LDAP, and FILE. Type man curl in the Terminal for complete details. The important thing to come away with here is that you can execute command line commands and then process the results all from within your Perl script! Note the substitution of the $url variable in the string assignment of the $sysstring variable. The $sysstring variable ends up as 'curl -s http://www.cnn.com/' after this substitution.

Next we declare a $count variable to number the items we find and then use the print command to write some text to the Terminal so anyone running our script can follow along as it executes.

The open command opens the $sysstring variable for reading (hence the | symbol following $sysstring). Open can be used to open files too but in this case it is smart enough to execute the curl command line embedded in the $sysstring variable. Once executed, we can read the data returned by curl by referencing the FILEHANDLE named FOO. A FILEHANDLE, in this case, is an I/O (input/output) connection between the Perl script and the output of curl. Once we have the output available in FOO, we can use a standard while loop to examine each line. The $lineout variable is assigned the $_ variable, which is a special variable that while returns as it extracts each line - $_ contains the last line extracted. If you were to add print "$lineout"; at this point you would see each line in the Terminal.

Next we search the line for each item in our array of search strings. The foreach statement does just what it says. For each item in the array @a, we are going to place it into a variable named $search. At this point we use the =~ matching operator to search $lineout for the $search string. If the text is found, the print command is executed and we display what we found. We happen to be doing a case sensitive search here but you can change that if you like. Don't be afraid of the =~ stuff, this is just a fancy way to say "find this". If you are interested in researching this, it's all part of a topic larger than what can be covered in this article: regular expressions.

Once we've looped through each line $lineout and searched for each $search string within them, we close the FILEHANDLE FOO and the program is complete. Not too bad, huh? Here are some exercises for the reader: make the search case-insensitive; make the program return an individual total count of each search term found (ie: 2 Clinton, 5 Bush, 3 Cheney, 1 Gore); search an array of news sites for an array of search terms.

Perl CGI And Apache

Thus far we've discussed using Perl in scripts that run locally on your computer to perform some task. However, one very popular use of Perl is as an Apache CGI. Apache is one of the most popular web servers in use today, and it comes pre-installed with Mac OS X. A CGI is a program (written in Perl, C, C++, PHP, ASP, etc.) that runs on a web server. You create a web-based form that allows a user to interact with the CGI. Examples of CGIs include search engines, guest books, shopping carts, etc. Most any time you fill out a form on a web page and press the "Submit" button, you are calling a CGI.

Behind the scenes, the web server receives the information from the web page and passes all of the fields to the CGI for processing. The CGI might verify the data and then send an email, write the information to a database, or send an order to the shipping department so you can receive your new toy via FedEx overnight delivery. Most of the time the CGI will then return a web page saying "thank you: order processed!"

Apache alone isn't too smart; it knows how to serve a file to a client but not much more. By adding a CGI you can extend Apache in any way you desire to perform tasks that the developers of Apache could never have imagined you would need to perform. Perl is the perfect language to write your CGI as thousands of examples are available throughout the net. For more information on Apache, you can visit http://www.apache.org/. For more information on specifically using Perl with Apache, you can visit http://perl.apache.org/.

Extending Perl

We discussed how Perl can be used to extend Apache, but what about extending Perl itself? The standard installation of Perl comes with hundreds of "built-in" functions that will meet many of your needs, however it also supports something called modules for those times when you need a little more. A module is like a library in C. Modules may be written in Perl or in C or C++ but that is transparent to the user of the module. A module usually concentrates on the support of a particular task. There are modules that support Internet protocols, encryption schemes, scientific and mathematical algorithms, image manipulation, audio, and much more.

You can create your own modules or you can download thousands (yes, thousands!) of them that currently exist from CPAN, the Comprehensive Perl Archive Network (at http://cpan.org/). CPAN contains not only modules but many sample Perl scripts and the Perl distributions themselves. It covers many too many things to discuss in this article, so you should visit the web site to explore for yourself.

Where To Go From Here?

Hopefully this article has given you a spark to go pursue Perl on your own. There are some excellent web sites to help you learn the intricacies of Perl. Make sure to visit http://www.perl.com/, which is a great place to read articles and learn more about Perl. All of the documentation is available online for you to read. Also be sure to visit http://www.perl.org/ and http://learn.perl.org/. There are also plenty of books available as well. Now that you have a short introduction to Perl, look for more articles in these pages to introduce you to complete real-world examples of what you can do with Perl under Mac OS X!


Joe Zobkiw is a software developer, musician and author living in Raleigh, NC. He has been a Macintosh user since 1986 and has owned no less than a baker's dozen Macintosh computers. He is currently keeping busy on a PowerBook G4 running OS X and rediscovering the command line. You can email Joe at zobkiw@triplesoft.com between 9am and 5pm ET M-F.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Adobe Photoshop 25.2 - Professional imag...
You can download Adobe Photoshop as a part of Creative Cloud for only $54.99/month Adobe Photoshop is a recognized classic of photo-enhancing software. It offers a broad spectrum of tools that can... Read more
PDFKey Pro 4.5.1 - Edit and print passwo...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
OnyX 4.5.3 - Maintenance and optimizatio...
OnyX is a multifunction utility that you can use to verify the startup disk and the structure of its system files, to run miscellaneous maintenance and cleaning tasks, to configure parameters in the... Read more
CrossOver 23.7.0 - Run Windows apps on y...
CrossOver can get your Windows productivity applications and PC games up and running on your Mac quickly and easily. CrossOver runs the Windows software that you need on Mac at home, in the office,... Read more
MacCleanse 12.5 - $29.95 (75% off)
MacCleanse is the product of thousands of hours of intense research and development. It meticulously scans all of the nooks and crannies of a computer for unnecessary junk that can take up huge... Read more
BetterTouchTool 4.333 - Customize multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom)... Read more
LibreOffice 7.6.3.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
CleanMyMac X 4.14.5 - Delete files that...
CleanMyMac X makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused... Read more
Chromium 121.0.6152.0 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. List of changes available here. Version for Apple... Read more
Tor Browser 13.0.5 - Anonymize Web brows...
Using Tor Browser you can protect yourself against tracking, surveillance, and censorship. Tor was originally designed, implemented, and deployed as a third-generation onion-routing project of the U.... Read more

Latest Forum Discussions

See All

‘Dysmantle’ Pets & Dungeons DLC Now...
Open world survival and crafting adventure game Dysmantle ($9.99) was one of our favorite games of 2022, and has gotten quite a bit of support with free and paid content since launching. Its newest content pack, the Pets & Dungeons DLC,... | Read more »
The ‘Among Us’ Indie Cosmicube Update Br...
After a bit of teasing, the huge Among Us (Free) Indie Cosmicube update featuring some notable collaborations is now live. These include some of my favorite indie games like Untitled Goose Game, Celeste, and Crypt of the Necrodancer. The update... | Read more »
Postknight 2 celebrates its second anniv...
It has been two years since Postknights 2 graced mobile, which should be an event all about the prizes and events, but unfortunately, it comes with the worst event name I have seen and I'm mad about it. To celebrate the anniversary, and thank all... | Read more »
‘Dissidia Final Fantasy Opera Omnia’ Is...
Square Enix just announced that Dissidia Final Fantasy Opera Omnia (Free) will be shutting down at the end of February 2024. | Read more »
SwitchArcade Round-Up: Reviews Featuring...
Hello gentle readers, and welcome to the SwitchArcade Round-Up for November 28th, 2023. In today’s article, we’ve got a little slice of news before we head into another parade of reviews. Our pal Mikhail has his takes on Spirittea, Salt &... | Read more »
Razer Kitsune Arcade Controller Review –...
Somebody once told me that leverless controllers for fighting games were a gimmick or cheating. I didn’t really know what they meant because I had only just started dipping my toes into the world of fight sticks with the 8BitDo Arcade Stick for... | Read more »
‘Gubbins – It’s A Word Game’ Review – So...
Is that the full title then? Gubbins – It’s A Word Game (Free)? I’m just going to call it Gubbins from here on out. If I need to talk about normal gubbins, I’ll write it without the capital letter G like I just did there. But I don’t have an old... | Read more »
New ‘Pizza Hero’ Update Adds Endless Mod...
Vampire Survivors-like Pizza Hero has been one of the more interesting takes on the genre on mobile. Since launch, it has also been updated a few times bringing in new content and features based on player feedback, and it has gotten a major update... | Read more »
The PMGC Grand Finalists are locked in w...
It has been a week of tremendous tension and spectacular shots, but the 2023 PUBG Mobile Global Championship has whittled down the 24 hopefuls to just five. These will take a step towards the grand final and a chance to win a piece of the $3... | Read more »
‘Titan Quest: Ultimate Edition’ With All...
Well it happened again. A new version of Titan Quest is available on mobile. But, it isn’t a problem for existing owners. This is technically the fifth iteration of Titan Quest as detailed by Jared here. | Read more »

Price Scanner via MacPrices.net

Cyber Week deals continue on Walmart’s online...
Walmart has Apple’s 9th generation 10.2″ iPads on sale for $80 off MSRP on their online store as part of their Cyber Week sale. Their prices are the lowest new prices available for iPads anywhere: –... Read more
Cyber Week Sale: Take $210-$240 off 16-inch M...
Apple retailer Expercom has 16-inch M3 Max MacBook Pros on Cyber Week sale for up to $240 off MSRP. Shipping is free. These are currently the best prices available anywhere for these M3 Max beasts... Read more
14-inch M3 MacBook Pro on Cyber Week sale for...
Amazon has the Silver 14″ M3 MacBook Pro on sale for $100 off MSRP today, only $1499. Shipping is free. Their price is currently the lowest available for a new M3-powered 14″ MacBook Pro among Apple’... Read more
13-inch M2 MacBook Airs are on Cyber Week Sal...
Apple retailers have the 13-inch M2 MacBook Air on Cyber Week sale for $150 off MSRP. Prices start at $949. These are the lowest 13-inch M2 MacBook Air prices available this week anywhere: (1): B... Read more
Cyber Week Sale: 15-inch M2 MacBook Airs for...
B&H Photo has Apple’s new 15″ MacBook Airs with M2 CPUs (8GB RAM/256GB SSD) in stock today and on sale for $1199 in all four colors. They have 15″ MacBook Airs (8GB RAM/512GB SSD) on sale for $... Read more
Apple Studio Display with Standard Glass now...
Amazon has the standard-glass Apple Studio Display on sale for $140 off MSRP for a limited time. Shipping is free: – Studio Display (Standard glass): $1459 $140 off MSRP Their price is the lowest... Read more
Find the best Holiday sales and deals on Appl...
Our Apple award-winning price trackers are the best place to look for the lowest prices and latest sales on all the latest Apple gear this Holiday shopping season. Scan our price trackers for the... Read more
Cyber Monday Flash Sale: Select Apple 15-inch...
As part of their Cyber Monday sale, B&H Photo has Apple’s new 15″ MacBook Airs with M2 CPUs (8GB RAM/256GB SSD) in stock today and on sale for $1029 in (at the time of this post) Space Gray and... Read more
Cyber Monday Flash Sale: Apple M2 Mac mini fo...
B&H Photo has Apple dropped their Cyber Monday sale price on the base M2 Mac mini another $20 to $479, $120 off Apple’s MSRP. That’s the cheapest price for a new Mac this Cyber Monday anywhere.... Read more
Apple Watch SE GPS models on Cyber Monday sal...
Walmart has Apple Watch SE GPS-only models on sale for $70 off MSRP today, each including free shipping, as part of their Cyber Monday sale. Their prices are the lowest currently available for SE... Read more

Jobs Board

IN6728 Optometrist- *Apple* Valley, CA- Tar...
Date: Nov 16, 2023 Brand: Target Optical Location: Apple Valley, CA, US, 92308 **Requisition ID:** 824398 At Target Optical, we help people see and look great - and Read more
Machine Operator 4 - *Apple* 2nd Shift - Bon...
Machine Operator 4 - Apple 2nd ShiftApply now " Apply now + Start apply with LinkedIn + Apply Now Start + Please wait Date:Nov 24, 2023 Location: Swedesboro, NJ, US, Read more
*Apple* Technician - Randstad US (United Sta...
apple technician. + burbank , california + posted november 15, 2023 **job details** summary + $30 - $34 per hour + temp to perm + bachelor degree + category computer Read more
Operations Associate - *Apple* Blossom Mall...
Operations Associate - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Read more
Cashier - *Apple* Blossom Mall - JCPenney (...
Cashier - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Blossom Mall Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.