Home > Articles

Perl 5: Learning to Read and Write

Learn the new features of Perl 5 in this sample chapter by Chris Bellew, Micah Brown, and Dan Livingston. They teach you how to read external files, how to automate articles, and how to write to external files.
This sample chapter is excerpted from Essential Perl 5 for Web Professionals, by Chris Bellew, Micah Brown, and Dan Livingston.

Let's say you walk into work one Monday morning ready to continue your work as a page layout designer for the upscale Stitch Magazine. As you take your first sip of coffee your phone rings and it's the president of the company on the other line. He starts rambling on and on about some brainstorm that he and the upper management team had over the weekend about taking the magazine and putting it up on the Web for millions to see!

You start to tell him, "Uh sir, are you sure you dialed the right extension? I really don't know how to do that." So, of course, he tells you to figure it out. How hard can it be? For the rest of the week you study the wonderful and challenging world of HTML and page layout design with such books as Essential Photoshop 5 for Web Professionals, and learn the intricacies of setting up a Web site for Stitch.

After you've spent a couple of weeks learning HTML and designing an online version of your company's magazine, you have a pretty nice-looking site and decide to call your boss and brag about it. When he gets back to you he says, "Great, great! But we need more! We need to have a user response form, a message board, a place where people can vote on questions posed in articles, search engines, monkeys flying across the screen and juggling the images around." You tell him you'll jump right on it, knowing that bonuses are just around the corner.

Being one of those brilliant people, you pick up this book, Essential Perl 5 for Web Professionals, and thumb through it. This book will teach you how to do everything your boss wants you to do to the company's site and more (with the exception of his reference to monkeys, but you think you'll figure out what the heck he was talking about later).

To start this chapter off, you're going to have to learn a few functions. After you learn some of these you will be able to work with the scripts that follow.

New Features


print is used for exactly what it says, to print information to STDOUT (standard output) or an alternate output. This can be what is printed to the screen, a file, or another program.


With Perl there are only three types of variables, unlike other languages, which may have many types.

  • Scalar
  • Array
  • Associative array

A scalar is a single value that is assigned information, whether it be an integer or a sentence. A scalar variable starts with a $ to distinguish itself from the other types of variables such as the array, which uses a @, or the associative array, which uses a %.


$someValue = 5;
$someName = "This sentence is assigned to the variable 
to the left";


There are two types of quotes you will be dealing with: single ('') and double ("").

Single quotes

These are very literal quotes. If you would like to print out a variable and you put it between single quotes, the actual variable name will be printed instead of the actual value.


print 'I'm thinking of the number: $number';

Result: I'm thinking of the number: $number

What you see between the single quotes is what you get—WYSIWYG.

Double quotes

Double quotes are a little friendlier than the single quotes in that they aren't quite as literal. If the scalar variable $number were assigned the value 5, here's what the result would look like:


print "I'm thinking of the number: $number";

Result: I'm thinking of the number: 5

Double quotes will also allow you to use special characters like the newline character \n to start a new line, whereas single quotes will actually just print \n.


You probably noticed the semicolon (;) at the end of some of these lines. This is to let Perl know that the end of that statement has been reached and it's time to start a new one.


The open function allows you to open a file to read, write, or append to. You can also use this function to open a process such as sendmail through a pipe (|), which you will get a look at in the next chapter.


Opening a file:


Opening a process:

open(FILEHANDLE, "|/usr/sbin/sendmail");


FILEHANDLES are used as unique identifiers, or labels, when accessing other files when opening, closing, editing, or doing anything with those files. Their names usually appear in uppercase letters; this is not necessary, as they will work in lowercase as well. As a proper rule, however, you should use uppercase.


open(ARTICLE1, ">article1.txt");

When referring to article1.txt you will use the ARTICLE1 as the FILEHANDLE.


print ARTICLE1 "this will be added to article1.txt";


You can give FILEHANDLEs any name you wish, other than those used by the Perl language.


Whenever you open a file or a process, it is usually good practice to close it when you are finished using it. This is not required, but not doing so could produce some problems.


Closing a file:


Closing a process:

open(FILEHANDLE, "|/usr/sbin/sendmail");


With the while statement, we take a variable that has earlier been assigned a value and test it to see whether it is true or not. This is called the condition. If the condition of the variable is true, then the statement will be executed. If the condition of the variable is false, then the statement after the while will be ignored and we move on to the next part of the code.


  ( statements );

The special $_ variable

Perl has a special variable for use in many different operations, such as the current line of a loop that is reading the contents of a FILEHANDLE, or a number of regular expression matches. In the case of a loop (while, foreach, and so forth), Perl automatically copies the current line being read into $_. This can save a lot of typing when using other operations when one or more parameters are $_. You will learn how we use $_ in the many examples in this book.

Escape Sequences

These are sequences of characters that consist of a backslash (\) followed by one or more characters that perform certain duties, as shown in Table 1–1. The most common one you will see is \n, which formats a new line. When you use the backslash, the character that follows it performs some action. If you want to actually print the character \, then you simply throw a \ in front of that: \\.

TABLE 1–1 Escape Sequences

Escape Sequence



Bell or a beep






Form feed


Force the next character into lowercase


Force all following characters into lowercase




Carriage return




Force the next character into uppercase


Force all following characters into uppercase


Vertical tab

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020