Beginning perl programming self study guide student manual 2018 19 edition

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Beginning Perl Programming

Self-Study Guide &

Student Manual

2018-19 Edition

William "Bo" Rothwell

A publication by

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This publication contains proprietary and confidential information, which is the property of One Course Source, Inc No part of this publication is be reproduced, copied, disclosed, transmitted, stored in a retrieval system or translated into any human or computer language, in any form, by any means, in whole or in part, without the prior express written consent of One Course Source

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OF DAMAGE, AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ARISING OUT

OF OR IN CONNECTION WITH THE USE OF THIS INFORMATION

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This notice may not be removed or altered

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2.1 Numeric Literals 39 2.2 Manipulating Numbers 40 2.3 String Literals 43 2.4 Manipulating Strings 44 2.5 Strings vs Numbers 48 2.6 Single vs Double Quotes 52 2.7 Scalars Variables 56 2.8 Undefined variables 57 2.9 Auto increment and Auto decrement 61 2.10 Reading data from the user 66 2.11 chomp & chop 67 2.12 Curly braces 70 2.13 Additional Resources 71 2.14 Lab Exercises 72

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3.1 Array Variables 74 3.2 Referencing Array Elements 75 3.3 Adding & removing elements in an array 79 3.4 The splice function 82 3.5 Using for loops 85 3.6 Using foreach loops 87 3.7 The reverse statement 91 3.8 The sort operator 92 3.9 The qw and qq statements 95 3.10 Arrays used in scalar context 96 3.11 Additional Resources 97 3.12 Lab Exercises 98

4.1 Associative Array Variables 100 4.2 Creating associative arrays 102 4.3 Accessing values with keys and foreach 105 4.4 Accessing values with "while-each" loops 107 4.5 The values statement 112 4.6 Reverse searching an associative array 114 4.7 Removing associative array keys and values 115 4.8 exists vs defined 116 4.9 Special Variables 119 4.10 The Environment Variables 120 4.11 The Argument Variable 122 4.12 Additional Resources 123 4.13 Lab Exercises 124

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5.1 Blocks 126 5.2 The if Statement 127 5.3 The unless Statement 133 5.4 The switch statement 134 5.5 The given statement 137 5.6 The while Statement 139 5.7 The until Statement 173 5.8 The do Statement 141 5.9 Loop control: last 144 5.10 Loop control: next 148 5.11 Additional Resources 149 5.12 Lab Exercises 150

6.1 Numeric Comparison 152 6.2 String Comparison 153 6.3 Difference between string and numeric comparison 155 6.4 Pattern Matching 158 6.5 Using the Outcome of a Statement 159 6.6 File Test Conditions 161 6.7 Complex Conditional Expressions 165 6.8 Understand and/or versus &&/|| 168 6.9 Using parentheses 170 6.10 Short circuiting 171 6.11 Additional Resources 173

6.12 Lab Exercises 174

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7.1 Reading Input 176 7.2 while & until Loops 177 7.3 Record Separator Variable 179 7.4 The Diamond Operator 181 7.5 The Default Variable 184 7.6 Using parentheses 186 7.7 Additional Resources 187 7.8 Lab Exercises 188

8.1 Filehandles 190 8.2 The die and warn Statements 191 8.3 Opening and Reading from Files 195 8.4 Opening and Writing to Files 198 8.5 Reading a Block of a Filehandle 200 8.6 Reading a Single Character 202 8.7 Piping in Perl 203 8.8 The format Statement 207 8.9 Here Documents 219 8.10 Additional Resources 222 8.11 Lab Exercises 223

9.1 Pattern Matching vs Wildcards 225 9.2 Matching, Substituting and Translation 226 9.3 Modifiers 229 9.4 Regular Expressions: Metacharacters 232 9.5 Regular Expressions: Classes 249 9.6 Regular Expressions: Backreferencing 256 9.7 Additional Resources 263 9.8 Lab Exercises 264

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10.1 split 266 10.2 join 270 10.3 substr 272 10.4 index 275 10.5 rindex 276 10.6 grep 278 10.7 srand & rand 280 10.8 sleep 282 10.9 Additional Resources 284 10.10 Lab Exercises 285

11.1 Controlling the Filesystem within Perl 287 11.2 Working with Directories 289 11.3 Working with Files 294 11.4 Back-Quoting 298 11.5 The System Statement 299 11.6 Additional Resources 301 11.7 Lab Exercises 302

12.1 Creating Functions 304 12.2 Invoking Functions 305 12.3 Returning Values from Functions 307 12.4 Passing Parameters 310 12.5 Scope of Variables 314 12.6 local() vs my() 316 12.7 Additional Resources 324 12.8 Lab Exercises 325

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13.1 What are Modules? 327 13.2 Loading Modules with use 328 13.3 Other functions of use 330 13.4 Additional Resources 335 13.5 Lab Exercises 336

14.1 The -w switch 338 14.2 The Perl Debugger 341 14.3 Debugger Commands 342 14.4 Additional Resources 343 14.5 Lab Exercises 344

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Introduction About this course

This manual was designed with the goal of assisting instructors in their

efforts of teaching students to be able to create Perl programs

Typographical syntax

Examples in this text of commands will appear in bold text and the output

of the commands will appear in italic text The commands and the output

of the commands will be placed in a box to separate them from other text

Example:

[student@ocs student]$ pwd

/home/student

Note: "[student@ocs student]$" is a prompt, a method the shell uses to

say “I’m ready for a new command”

Bold text within a sentence will indicate an important term or a command

Files and directories are highlighted by being placed in courier font

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Using this manual while in class

In many ways, class manuals are different from textbooks Textbooks are

often filled with lengthy paragraphs that explain a topic in detail

Unfortunately, this style doesn’t work well in a classroom environment

Class manuals often are much more concise than textbooks It's difficult to

follow the instructor’s example and read lengthy paragraphs in a book at

the same time For this purpose, class manuals are often more terse

Lab Exercises

The lab exercises provided in this class are intended to provide practical,

hands on experience with programming Perl Students are strongly

encouraged to perform the labs provided at the end of each Unit to

reinforce the knowledge provided in class

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Resources

In each unit, resources are provided to provide the learner with a source

for more information These resources may include online documentation,

local (on your system) documentation and traditional books

Due to the fact that these resources changes (especially online resources),

we provide these resources on our web site instead of printing them in our

courseware This allows us to provide updated resources in a timely

manner

For this class, the resources can be found here:

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Using the Perl debugger

During this course the Perl debugger is used to demonstrate techniques

To enter the Perl debugger to test Perl code, use the following:

ocs% perl -d -e "1;"

Loading DB routines from perl5db.pl version 1.32

Editor support available

Enter h or `h h' for help, or `perldoc perldebug' for more help

main::(-e:1): 1;

DB<1>

Note: if you installed Active State's ActivePerl, you might end up in their

GUI-based debugger To temporarily change your system to use the

built-in Perl debugger, enter the followbuilt-ing command(s) built-in your shell:

Windows

set PERL5DB=BEGIN { require 'perl5db.pl'; }

set PERLDB_OPTS=

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Linux

export PERLDB_OPTS=

To re-enable the PDK debugger, set the PERL5DB variable to an empty

string

A note about this course content

In most cases it is best to use the latest version of Perl However, using

the latest version is not always going to be possible Many students who

follow this course or take official OCS classes will be in an environment

that uses an older versions of Perl (sometimes a much older version)

There are a variety of reasons (being stuck on an older OS platform,

needing a feature that only exists in an older version of Perl, stubborn IT

managers, etc.) why you may be required to use an older version of Perl

This was taken into consideration when this manual was written While the

newer Perl techniques are covered in this class and are normally more

effective, the course also presents older techniques Not only does this

help support Perl programmers who are stuck in older versions of Perl, but

it also helps Perl programmers who have been called upon to maintain (or

update) older Perl scripts

In addition, there are many things in Perl that can be accomplished in more

than one way While not every single method is provided in this course, we

do try to show different common ways of performing tasks This makes it

easier for you to read other Perl scripts that may have used a different

technique than what you are using

Perl is well known for being a flexible programming language While there

are some advantages of this, it does require exploring more techniques in

a course such as this one

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Try it!

Throughout the course, you will see boxes like this one The purpose of

these boxes is to encourage you to try a new skill that is being taught

Keep in mind that in an instructor-led classes, these boxes may be ignored

by the instructor The benefit of these boxes is for self-study learners or for

learners who are reviewing the materials after the end of the instructor-led

class

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Unit One Meet Perl

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1.2 Perl development environments

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Which derivative for *nix?

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Which derivative for Windows?

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Pick your Perl development tools

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Understanding Perl versions

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The interactive method (debugger)

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Note: if you installed Active State's ActivePerl, you might end up in their

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The script method

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UNIX-based operating systems provide you another method of executing

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regarding Perl is found

under the "Manual"

section

When you want to view

documentation about a

specific function, variable

or feature, look under the

Reference section

Standard modules (which are like libraries), have documentation that can

be viewed under the Modules section

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In addition to the web-based documentation, you can access

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On Windows, execute the command perldoc perl:

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If you review the main documentation page (perldoc perl), you will discover

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To see documentation on a specific builtin function, use the -f option with

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1.6 Perl Resources

In each unit, resources are provided to provide the learner with a source

for more information These resources may include online documentation,

local (on your system) documentation and traditional books

Due to the fact that these resources changes (especially online resources),

we provide these resources on our web site instead of printing them in our

courseware This allows us to provide updated resources in a timely

manner

For this unit, the resources can be found here:

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1.7 Lab Exercises

A note about the lab exercises in this class: Creating lab exercises that

will be beneficial to all students can be difficult Lab exercises that focus

on specific scenarios (such as engineering test cases) can result in

difficulties for students who do not perform this sort of programming As a

result, we focused on creating labs that will perform tasks that are fairly

generic, but that also assist the student in practicing the new skills that are

learned in class In addition, to make the lab exercises more realistic, we

attempt to build on one script throughout class rather than build many,

small scripts

Throughout this course, you will build on a script called "cb.pl"

This script will eventually be a simple (flat) database program that will be

customized to fit simple database needs To make it specific for the class,

we will make it a database that contains checkbook entries

For this lab, create a file called cb1.pl and perform the following functions:

1 Create comments at the beginning of the code that indicate what the

program does (handles deposits, withdrawals, checks writing, looks

up checks by check number or date written, and prints a statement)

and other data (author, date/time, version (1.1))

2 Using the print statement, have the program produce the following

output when it is run:

Welcome to checkbook 1.1

Please enter your name:

When you have completed your work, compare your script against the

cb1.pl file provided in lab answers During the instructor-led classes, the

instructor may review the answer script and provide you with the

opportunity to ask questions

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Unit Two Scalar Variables

2.9 Auto increment and Auto decrement 61

2.10 Reading data from the user 66

2.11 chomp & chop 67

2.12 Curly braces 70

2.13 Additional Resources 71

2.14 Lab Exercises 72

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operators can only be used

on scalar variables (not constant numbers)

Auto decrement See later

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