Perl How to Program : Introducing CGI and Python

by Deitel, Harvey M.; Deitel, Paul J.; Nieto, Tem R.; McPhie, D. C.

• ISBN13: 9780130284181
• ISBN10: 0130284181
• Edition: CD
• Format: Paperback
• Copyright: 2001-01-25
• Publisher: Prentice Hall
• More Book Details
• Purchase Benefits

Summary

This new book by the world's leading programming language textbook authors carefully explains how to use Perl as a general-purpose programming language and how to program multi-tier, client/server, database-intensive, Internet-and-Web-based applications. Dr. Harvey M. Deitel and Paul J. Deitel are the principals of Deitel & Associates, Inc., the internationally recognized corporate training and content-creation organization specializing in C++, Javatrade;, C#, C, Visual Basicreg;, XMLtrade;, Python, Perl, Internet, World Wide Web and object technologies. The Deitels are also the authors of the world's #1 Java and C++ textbooks, Java How to Program, 3/e and C++ How to Program, 3/e. In Perl How to Program, the Deitels and their colleagues, Tem R. Nieto and David C. McPhie, discuss topics you need to build complete, Web-based applications including: CGI/HTML forms/XML/CGI.pm Control Structures/Arrays/Hashes Regular Expressions/Strings Objects/Encapsulation OOP/Inheritance/References Database/DBI/SQL/Signals/Contexts Security/Accessibility Typeglobs/File Globbing Networking/Sockts/Internet Protocols Cookies/Session Tracking Filehandles/Data Structures Process Control/Forking/Piping Subroutines/Modules/Packages/Overloading Web Automation/OLE Automation Server-Side Includes/Ties/Closures Graphics/GUI/Perl/TK Perl How to Program includes extensive pedagogic features: Hundreds of LIVE-CODEtrade; programs with screen captures that show exact outputs Extensive World Wide Web and Internet resources to encourage further research Hundreds of tips, recommended practices and cautions-all marked with icons

Author Biography

Dr. Harvey M. Deitel, CEO of Deitel & Associates, Inc., has 40 years in the computing field including extensive industry and academic experience. He is one of the world's leading computer science instructors and seminar presenters. Dr. Deitel earned B.S. and M.S. degrees from the Massachusetts Institute of Technology and a Ph.D. from Boston University. He has 20 years of college teaching experience including earning tenure and serving as the Chairman of the Computer Science Department at Boston College before founding Deitel & Associates, Inc. with his son Paul J. Deitel. He is author or co-author of several dozen books and multimedia packages and is currently writing many more. With translations published in Japanese, Russian, Spanish, Elementary Chinese, Advanced Chinese, Korean, French, Polish and Portuguese, Dr. Deitel's texts have earned international recognition. Dr. Deitel has delivered professional seminars internationally to major corporations, government organizations and various branches of the military.

Paul J. Deitel, Executive Vice President of Deitel & Associates, Inc., is a graduate of the Massachusetts Institute of Technology's Sloan School of Management where he studied Information Technology. Through Deitel & Associates, Inc. he has delivered Internet and World Wide Web courses and programming language classes for industry clients including Compaq, Sun Microsystems, White Sands Missile Range, Rogue Wave Software, Computervision, Straws, Fidelity, Cambridge Technology Partners, Lucent TecItnologies, Adra Systems, Entergy, CableData Systems, NASA at the Kennedy Space Center, the National Severe Storm Laboratory, IBM and many other organizations. He has lectured on for the Boston Chapter of the Association for Computing Machinery, and has taught satellite-based courses through a cooperative venture of Deitel & Associates, Inc., Prentice Hall and the Technology Education Network. He and his father, Dr. Harvey M. Deitel, are the world's best-selling Computer Science textbook authors.

Tem R. Nieto, Director of Product Development with Deitel & Associates, Inc., is a graduate of the Massachusetts Institute of Technology where he studied engineering and computing. Through Deitel & Associates, Inc. he has delivered courses for industry clients including Sun Microsystems, Compaq, EMC, Stratus, Fidelity, Art Technology, Progress Software, Toys "R" Us, Operational Support Facility of the National Oceanographic and Atmospheric Administration, Jet Propulsion Laboratory, Nynex, Motorola, Federal Reserve Bank of Chicago, Banyan, Schlumberger, University of Notre Dame, NASA, various military installations and many others. He has co-authored several books and multimedia packages with the Deitels and has contributed to virtually every Deitel & Associates, Inc. publication.

David Craig McPhie recently graduated from Harvard College magna cum laude with a B.A. in Physics, having completed extensive computer science course work in C, C++, Java and Lisp. His course work included a final project using CGI to implement an online word game ("Elggob") that won accolades from his instructors and peers. Prior to collaborating on Perl How to Program, David programmed a Monte Carlo electron path modeling application for AlliedSignal, Electron Vision Group in San Diego. His other computing experience includes software test script writing and implementation with SilkTest at Cakewalk Software, and debugging courtroom simulation software code at the Education Technology Department of Harvard Law School. David has now changed venues and is studying law at Harvard Law School. He maintains an interest in technology law, and continues to use Per in Web programming for student organizations. He and his wife Erin and daughter Emily live in Cambridge, MA.

Table of Contents

Contents	vii
Illustrations	xviii
Preface	xxx
Introduction to Computers, the Internet and the World Wide Web	1	(25)
Introduction	2	(1)
What Is a Computer?	3	(1)
Computer Organization	4	(1)
Evolution of Operating Systems	5	(1)
Personal Computing, Distributed Computing and Client/Server Computing	5	(1)
Machine Languages, Assembly Languages and High-level Languages	6	(1)
Structured Programming	7	(1)
Object-Oriented Programming	8	(1)
Hardware Trends	9	(1)
History of the Internet	10	(1)
History of the World Wide Web	11	(1)
History of Perl	11	(2)
Perl Library	13	(1)
General Notes About Perl and This Book	13	(1)
A Tour of the Book	13	(9)
Internet and World Wide Web Resources	22	(4)
Introduction to Programming in Perl	26	(34)
Introduction	27	(1)
Simple Programs that Display Lines of Text	27	(5)
A Simple Program: Printing a Line of text	27	(2)
Executing the Program	29	(1)
A Simple Program: Printing Several Lines of Text	30	(2)
Another Simple Program: Adding Two Integers	32	(2)
Memory Concepts	34	(1)
Scalar Values and Scalar Variables	35	(1)
Arithmetic Operators	36	(4)
Assignment Operators	40	(1)
Increment and Decrement Operators	41	(2)
Decision Making: Equality and Relational Operators	43	(4)
Confusing Equality (==) and Assignment (=) Operators	47	(2)
String Operators	49	(1)
Numeric and String Contexts	50	(2)
Internet and World Wide Web Resources	52	(8)
Control Structures: Part I	60	(34)
Introduction	61	(1)
Algorithms	61	(1)
Pseudocode	62	(1)
Control Structures	62	(2)
if and unless Selection Structures	64	(3)
if/else and if/elsif/else Selection Structures	67	(3)
while and until Repetition Structures	70	(2)
do/while and do/until Repetition Structures	72	(2)
Formulating Algorithms: Case Study 1 (Counter-controlled Repetition)	74	(3)
Formulating Algorithms with Top-down, Stepwise Refinement: Case Study 2 (Sentinel-controlled Repetition)	77	(5)
Formulating Algorithms with Top-down, Stepwise Refinement: Case Study 3 (Nested Control Structures)	82	(4)
Internet and World Wide Web Resources	86	(8)
Arrays and Hashes	94	(41)
Introduction	95	(1)
Additional Data Types	95	(1)
Lists and List Context	96	(1)
Arrays	96	(3)
Creating and Manipulating an Array	99	(1)
Repetition with the for Structure	100	(3)
Additional Examples of Creating Arrays	103	(4)
Array Manipulation	107	(4)
Array Functions	111	(4)
List Functions	115	(1)
Searching Sorted Arrays	116	(6)
Linear Search	116	(2)
Binary Search	118	(4)
Introduction to Hashes	122	(1)
Creating and Manipulating a Hash	122	(3)
Hash-related Functions	125	(4)
Internet and World Wide Web Resources	129	(6)
Control Structures: Part II	135	(35)
Introduction	136	(1)
foreach Repetition Structure	136	(3)
Special Variable $_	139	(1)
Loop Control Shortcuts: grep and map	140	(2)
Case Study: Computing Mean, Median and Mode	142	(4)
Loop Controls: The next Statement	146	(1)
Loop Controls: The last Statement	147	(1)
Loop Controls: The redo Statement	148	(1)
Block Labels	149	(1)
Bare Blocks	150	(1)
Logical Operators	151	(4)
Using Logical Operators for Flow Control	155	(2)
Error Functions: die and warn	157	(1)
Summary of Structured Programming	158	(12)
Subroutines and Functions	170	(46)
Introduction	171	(1)
Subroutines in Perl	171	(2)
Built-in Math Functions	173	(1)
User-defined Subroutines	174	(2)
Argument Lists	176	(2)
Returning Values	178	(2)
Other Ways to Invoke a Subroutine	180	(3)
Random-Number Generation	183	(4)
Example: A Game of Chance	187	(3)
Recursion	190	(3)
Example Using Recursion: Fibonacci	193	(3)
Recursion vs. Iteration	196	(1)
Scope Rules: Global, Lexical and Dynamic	197	(3)
Namespaces, Packages and Modules	200	(6)
Defining a Package and Importing it with require	200	(3)
Modules and the use Statement	203	(2)
Other Features of the use Statement	205	(1)
Pragmas	206	(10)
Introduction to the Common Gateway Interface (CGI)	216	(37)
Introduction	217	(1)
A Simple HTTP Transaction	217	(3)
A Simple CGI Script	220	(4)
Using CGI.pm to Generate HTML	224	(3)
Sending Input to a CGI Script	227	(2)
Using HTML Forms to Send Input	229	(6)
Using CGI.pm to Create Forms and Read Input	235	(3)
Other Headers	238	(1)
Example: An Interactive Portal	239	(4)
Internet and World Wide Web Resources	243	(10)
Regular Expressions	253	(31)
Introduction	254	(1)
Matching Operator m//	254	(2)
Substitution Operator s///	256	(1)
Special Characters and Character Classes	257	(2)
Alternation	259	(2)
Quantifiers	261	(2)
Quantifier Greediness	263	(1)
Assertions	264	(2)
Backreferences	266	(3)
More Regular-Expression Modifiers	269	(1)
Global Searching and the /g Modifier	270	(1)
Example: Form Verification	271	(5)
Internet and World Wide Web Resources	276	(8)
String Manipulation	284	(35)
Introduction	285	(1)
Quotes and Quote Operators	285	(3)
``Here'' Documents	288	(2)
Basic String Functions	290	(2)
chop and chomp functions	292	(3)
index and rindex Functions	295	(2)
Function join	297	(1)
Function split	298	(2)
tr/// Translation Operator	300	(2)
Formatting Outputs with printf and sprintf	302	(3)
Printing with Field Widths and Precision	305	(2)
Using Flags in the printf Format Control String	307	(3)
Evaluating Strings as Perl Code	310	(9)
File Processing	319	(26)
Introduction	320	(1)
Data Hierarchy	320	(2)
Filehandles	322	(1)
Opening and Closing Filehandles	323	(2)
Using Filehandles	325	(2)
@ARGV Special Variable	327	(1)
Other Ways to Read from Files	328	(1)
Implementing a Random-Access File	329	(3)
Example: Web-Page Log Generator	332	(3)
Example: Guestbook	335	(2)
Internet and World Wide Web Resources	337	(8)
File and Directory Manipulation	345	(19)
Introduction	346	(1)
File Tests and sysopen	346	(3)
Permissions	349	(1)
File Manipulation	350	(3)
Hard Links and Symbolic Links	353	(1)
File Globbing	354	(1)
Directory Handles and Manipulation	354	(1)
Example: Web Site Recent-Update Page	355	(9)
Formatting	364	(35)
Introduction	365	(1)
Creating Formatted Reports	365	(3)
Top-of-Form Processing	368	(2)
Multiple-Line Format Fields	370	(3)
Format Variables	373	(4)
Case Study: Outputting a Database	377	(3)
Case Study: Web Log Analyzer	380	(19)
References	399	(40)
Introduction	400	(1)
References	400	(2)
References to Nonscalars	402	(3)
Anonymous Structures	405	(3)
Closures	408	(2)
References as Function Arguments	410	(4)
Nested Data Structures	414	(5)
Garbage Collection and Circular References	419	(1)
Symbolic References	420	(3)
Typeglobs	423	(4)
Referencing Filehandles	427	(2)
Uses for References	429	(3)
Internet and World Wide Web Resources	432	(7)
Objects and Modules	439	(39)
Introduction	440	(1)
Using a Class	441	(2)
Creating a Simple Class	443	(3)
Inheritance	446	(5)
Overriding Methods	451	(5)
Other Class Relationships: Multiple Inheritance, Composition and Containment	456	(2)
Base Class Universal	458	(1)
Encapsulation: Public vs. Private	459	(1)
Closure Method	460	(3)
Implicit Functions	463	(2)
Autoload Function	465	(3)
Tied Variables	468	(2)
Internet and World Wide Web Resources	470	(8)
Databases: SQL and Perl Database Interface (DBI)	478	(47)
Introduction	479	(1)
Relational Database Model	480	(1)
Relational Database Overview: Employee.mdb	481	(1)
Structured Query Language (SQL)	482	(9)
Basic Select Query	483	(1)
Where Clause	484	(2)
Order By Clause	486	(2)
Inserting a Record	488	(1)
Updating a Record	489	(1)
Deleting a Record	490	(1)
Introduction to DBI	491	(1)
Working with DBI	491	(3)
Manipulating a Database with DBI	494	(4)
DBI and the Web	498	(10)
DBI Utility Functions	508	(1)
MySQL Server	508	(10)
Internet and World Wide Web Resources	518	(7)
Session Tracking and Cookies	525	(34)
Introduction	526	(1)
Uses of Storing Data	526	(1)
Methods of Storing Data	526	(1)
Query Strings	527	(4)
Hidden Fields	531	(3)
Cookies	534	(4)
Server-side Files	538	(4)
Example: Shopping Cart	542	(17)
Web Automation and Networking	559	(29)
Introduction	560	(1)
Introduction to LWP	560	(1)
LWP Commands	561	(3)
The LWP::Simple Module	564	(1)
HTML Parsing	565	(2)
Introduction to Advanced Networking	567	(1)
Protocols	568	(1)
Transport Control Protocol (TCP)	568	(4)
Simple Mail Transfer Protocol (SMTP)	572	(3)
Post Office Protocol (POP)	575	(4)
Searching the World Wide Web	579	(9)
Process Management	588	(27)
Introduction	589	(1)
The fork command	590	(4)
The system and exec functions	594	(3)
Controlling the Input and Output of Processes	597	(4)
Communicating Between Processes	601	(3)
Signal Handling	604	(2)
Sending Signals	606	(2)
OLE Automation	608	(7)
Security	615	(69)
Introduction	616	(1)
What Makes a Program Insecure	617	(1)
Using User Data with Shell Commands	618	(4)
Defensive Programming	622	(2)
Taint Mode	624	(2)
Printing User Input to a Web Page	626	(6)
Denial-of-Service Attacks	632	(3)
Other Security Attacks	635	(3)
Using Hidden Fields	638	(6)
Introduction to Cryptography Theory	644	(1)
Using Encryption	645	(4)
Secret-key Cryptography	649	(2)
Public-Key Cryptography	651	(3)
Key Agreement Protocols	654	(1)
Key Management	654	(1)
Digital Signatures	655	(1)
Public-Key Infrastructure, Certificates and Certification Authorities	656	(2)
Cryptanalysis	658	(1)
Security Protocols	659	(2)
Secure Sockets Layer (SSL)	659	(1)
Secure Electronic Transaction™ (Set™)	660	(1)
Network Security	661	(2)
Firewalls	661	(1)
Kerberos	662	(1)
Biometrics	663	(1)
Steganography	663	(2)
Internet and World Wide Web Resources	665	(19)
Data Structures	684	(37)
Introduction	685	(1)
Self-referential Structures	685	(1)
Linked Lists	686	(10)
Doubly Linked Lists	696	(5)
Stacks and Queues	701	(3)
Trees	704	(7)
Hashes	711	(10)
Graphics/Tk	721	(22)
Introduction	722	(1)
GD Module: Creating Simple Shapes	722	(3)
GD Module: Image Manipulation	725	(1)
Chart Module	726	(2)
Introduction to GUI	728	(1)
Introduction to Tk	728	(2)
Tk: GUI Components	730	(4)
Tk Case Study: A GUI Application	734	(9)
Extensible Markup Language (XML)	743	(66)
Introduction	744	(1)
Perl and XML	745	(1)
Structuring Data	746	(6)
XML Namespaces	752	(2)
Document Type Definitions (DTD) and Schema	754	(5)
Document Type Definitions	754	(2)
W3C XML Schema	756	(3)
Customized Markup Languages	759	(3)
MathML	760	(1)
WML	761	(1)
XBRL	762	(1)
ebXML	762	(1)
FpML	762	(1)
Other Markup Languages	762	(1)
Document Object Model (DOM)	762	(2)
XML::DOM	764	(5)
DOM Methods	769	(3)
Simple API for XML (SAX)	772	(1)
Parsing XML with XML::Parser	773	(4)
Data::Dumper and XML	777	(1)
Extensible Style Language (XSL)	777	(5)
Generating XML in Perl	782	(2)
Case Study: Message Forums with Perl and XML	784	(16)
Displaying the Forums using XML::Parser	785	(4)
Using XML::DOM to Add Forums and Messages	789	(3)
Alterations for Non-XSL Browsers	792	(8)
Internet and World Wide Web' Resources	800	(9)
Accessibility	809	(26)
Introduction	810	(1)
Providing Alternatives for Multimedia Content	810	(9)
Maximizing Readability by Focusing on Structure	819	(1)
Accessibility in HTML Tables	820	(3)
Accessibility in HTML Frames	823	(1)
Using Voice Synthesis and Recognition with VoiceXML™	823	(4)
JAWS® for Windows	827	(1)
Other Accessibility Tools	828	(1)
Internet and World Wide Web Resources	828	(7)
Bonus: Introduction to HyperText Markup Language 4: Part I	835	(23)
Introduction	836	(1)
Markup Languages	836	(1)
Editing HTML	837	(1)
Common Elements	837	(3)
Headers	840	(1)
Linking	841	(3)
Images	844	(3)
Special Characters and More Line Breaks	847	(2)
Unordered Lists	849	(1)
Nested and Ordered Lists	850	(3)
Internet and World Wide Web Resources	853	(5)
Bonus: Introduction to HyperText Markup Language 4: Part II	858	(33)
Introduction	859	(1)
Basic HTML Tables	859	(3)
Intermediate HTML Tables and Formatting	862	(2)
Basic HTML Forms	864	(3)
More Complex HTML Forms	867	(7)
Internal Linking	874	(2)
Creating and Using Image Maps	876	(3)
<meta> Tags	879	(1)
frameset Element	880	(2)
Nested framesets	882	(2)
Internet and World Wide Web Resources	884	(7)
Bonus: Cascading Style Sheets™ (CSS)	891	(32)
Introduction	892	(1)
Inline Styles	892	(1)
Creating Style Sheets with the style Element	893	(3)
Conflicting Styles	896	(3)
Linking External Style Sheets	899	(2)
Positioning Elements	901	(3)
Backgrounds	904	(3)
Element Dimensions	907	(2)
Text Flow and the Box Model	909	(5)
User Style Sheets	914	(4)
Internet and World Wide Web Resources	918	(5)
Bonus: Introduction to Python Programming	923	(62)
Introduction	924	(2)
A first Python program	925	(1)
Python keywords	926	(1)
Basic Data Types, Control Structures and Functions	926	(5)
Tuples, Lists and Dictionaries	931	(5)
String Processing and Regular Expressions	936	(5)
Exception handling	941	(2)
Introduction to CGI programming	943	(2)
Form Processing and Business Logic	945	(6)
Cookies	951	(5)
Database Application Programming Interface (DB-API)	956	(4)
Setup	956	(1)
Simple DB-API program	956	(4)
Object-Oriented Programming	960	(2)
Case Study: GUI Database Application	962	(12)
Gadfly	962	(1)
Tkinter	963	(1)
Setup	963	(1)
GUI Database Viewer Implementation	964	(10)
Operator Precedence Chart	974	(1)
Internet and World Wide Web Resources	975	(10)
A HTML Special Characters	985	(1)
B HTML Colors	986	(3)
C ASCII Character Set	989	(1)
D Operator Precedence Chart	990	(3)
E Number Systems	993	(13)
E.1 Introduction	994	(3)
E.2 Abbreviating Binary Numbers as Octal Numbers and Hexadecimal Numbers	997	(1)
E.3 Converting Octal Numbers and Hexadecimal Numbers to Binary Numbers	998	(1)
E.4 Converting from Binary, Octal, or Hexadecimal to Decimal	998	(1)
E.5 Converting from Decimal to Binary, Octal, or Hexadecimal	999	(1)
E.6 Negative Binary Numbers: Two's Complement Notation	1000	(6)
F Career Resources	1006	(18)
F.1 Introduction	1007	(1)
F.2 Online Career Services	1008	(2)
F.3 Career Opportunities for Employees	1010	(4)
F.3.1 Comprehensive Career Sites	1010	(1)
F.3.2 Technical Positions	1010	(1)
F.3.3 Contracting Online	1011	(1)
F.3.4 Executive Positions	1012	(1)
F.3.5 Students and Young Professionals	1012	(1)
F.3.6 Other Online Career Services	1013	(1)
F.4 Online Opportunities for Employers	1014	(3)
F.4.1 Posting Jobs Online	1014	(1)
F.4.2 Diversity in the Workplace	1015	(1)
F.4.3 Recruiting Services	1016	(1)
F.4.4 Testing Potential Employees Online	1017	(1)
F.5 Internet and World Wide Web Resources	1017	(7)
G Perl 6 Web Resources	1024	(3)
G.1 Introduction	1024	(1)
G.2 Future of Perl	1024	(1)
G.3 Internet and World Wide Web Resources	1025	(2)
Bibliography	1027	(2)
Index	1029

Excerpts

PrefaceWelcome to Perl! This book is by an old guy and three young guys. The old guy (HMD; Massachusetts Institute of Technology 1967) has been programming and/or teaching programming for 40 years. The three young guys (PJD; MIT 1991, TRN; MIT 1992 and DCM Harvard 2000) have each been programming and/or teaching programming for many years. The old guy programs and teaches from experience; the young guys do so from an inexhaustible reserve of energy. The old guy wants clarity; the young guys want performance. The old guy seeks elegance and beauty; the young guys want results. We got together to produce a book we hope you will find informative, challenging and entertaining. Why We Wrote Perl How to ProgramDr. Harvey M. Deitel taught introductory programming courses in universities for 20 years with an emphasis on developing clearly written, well-designed programs. Much of what is taught in these courses is the basic principles of programming with an emphasis on the effective use of data types, control structures, arrays and functionalization. Our experience has been that students handle the material in this book in about the same manner as they handle it in introductory Pascal or C courses. There is one noticeable difference though: students are highly motivated by the fact that they are learning a leading-edge programming language and a leading-edge programming paradigm (object-based programming) that will be immediately useful to them as they leave the university environment and head into a world of e-business and e-commerce in which the Internet and the World Wide Web have a massive prominence.Our goal was clear: produce a textbook for introductory university-level courses in programming for students with little or no programming experience, yet offer the depth and the rigorous treatment of theory and practice demanded by traditional, upper-level programming courses to satisfy professionals' needs. To meet this goal, we produced a comprehensive book that patiently teaches the principles of control structures, object-based programming and Internet and World Wide Web programming in Perl. After mastering the material in this book, students will be well prepared to take advantage of the Internet and the Web as they take upper-level courses and venture into the rapidly changing business world.Perl How to Programis the ninth book in the Deitel/Prentice HallHow to Programseries. The key focus of this book is Web-based applications development. Our audiences want to build real-world, industrial-strength, Web-based applications. These audiences care about good looking Web pages. But they also care about client/server systems, databases and distributed computing.Many books about the Web are reference manuals with exhaustive listings of features. That is not our style. We concentrate on creating real applications. We provide the live-code examples on the CD accompanying this book so that you can run the applications and see the outputs.We are excited about the enormous range of possibilities the Internet and the Web offer. We performed extensive research for this book and located many Internet and Web resources (which we provide as live links on the CD-ROM that accompanies this book) to help you learn about Perl. These links include general information, tutorials and demonstrations.We have worked hard to create hundreds of useful live-code examples to help you master Perl programming quickly and effectively. All of the code examples are on the accompanying disk and are available for free download from our Web sites: www.deitel.com www.prenhall.com/deitelThe book's exercises range from simple recall questions to lengthy programming problems to major projects. Instructors requiring substantial term projects will find many appropriate problems listed in the exercises, especially in the la