book

Programming Perl, 3rd Edition

by Larry Wall, Tom Christiansen, Jon Orwant

July 2000

Intermediate to advanced

1104 pages

35h 1m

English

O'Reilly Media, Inc.

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Programming Perl, 3rd Edition
A Note Regarding Supplemental Files
Preface
The Pursuit of Happiness
What's New in This Edition
The Standard Distribution
Online Documentation
Navigating the Standard ManpagesSearching the ManpagesNon-Perl Manpages
Offline Documentation
Additional Resources
Perl on the WebUsenet NewsgroupsBug Reports
Conventions Used in This Book
Acknowledgments

We'd Like to Hear from You
I. Overview
1. An Overview of Perl
1.1. Getting Started
1.2. Natural and Artificial Languages
1.2.1. Variable Syntax1.2.1.1. Singularities1.2.1.2. Pluralities1.2.1.2.1. Arrays.1.2.1.2.2. Hashes.1.2.1.3. Complexities1.2.1.4. Simplicities1.2.2. Verbs
1.3. An Average Example
1.3.1. How to Do It
1.4. Filehandles
1.5. Operators
1.5.1. Some Binary Arithmetic Operators1.5.2. String Operators1.5.3. Assignment Operators1.5.4. Unary Arithmetic Operators1.5.5. Logical Operators1.5.6. Some Numeric and String Comparison Operators1.5.7. Some File Test Operators
1.6. Control Structures
1.6.1. What Is Truth?1.6.1.1. The if and unless statements1.6.2. Iterative (Looping) Constructs1.6.2.1. The while and until statements1.6.2.2. The for statement1.6.2.3. The foreach statement1.6.2.4. Breaking out: next and last
1.7. Regular Expressions
1.7.1. Quantifiers1.7.2. Minimal Matching1.7.3. Nailing Things Down1.7.4. Backreferences
1.8. List Processing
1.9. What You Don't Know Won't Hurt You (Much)
II. The Gory Details
2. Bits and Pieces
2.1. Atoms
2.2. Molecules
2.3. Built-in Data Types
2.4. Variables
2.5. Names
2.5.1. Name Lookups
2.6. Scalar Values
2.6.1. Numeric Literals2.6.2. String Literals2.6.3. Pick Your Own Quotes2.6.4. Or Leave the Quotes Out Entirely2.6.5. Interpolating Array Values2.6.6. "Here" Documents2.6.7. V-String Literals2.6.8. Other Literal Tokens
2.7. Context
2.7.1. Scalar and List Context2.7.2. Boolean Context2.7.3. Void Context2.7.4. Interpolative Context
2.8. List Values and Arrays
2.8.1. List Assignment2.8.2. Array Length
2.9. Hashes
2.10. Typeglobs and Filehandles
2.11. Input Operators
2.11.1. Command Input (Backtick) Operator2.11.2. Line Input (Angle) Operator2.11.3. Filename Globbing Operator
3. Unary and Binary Operators
3.1. Terms and List Operators (Leftward)
3.2. The Arrow Operator
3.3. Autoincrement and Autodecrement
3.4. Exponentiation
3.5. Ideographic Unary Operators
3.6. Binding Operators
3.7. Multiplicative Operators
3.8. Additive Operators
3.9. Shift Operators
3.10. Named Unary and File Test Operators
3.11. Relational Operators
3.12. Equality Operators
3.13. Bitwise Operators
3.14. C-Style Logical (Short-Circuit) Operators
3.15. Range Operator
3.16. Conditional Operator
3.17. Assignment Operators
3.18. Comma Operators
3.19. List Operators (Rightward)
3.20. Logical and, or, not, and xor
3.21. C Operators Missing from Perl
4. Statements and Declarations
4.1. Simple Statements
4.2. Compound Statements
4.3. if and unless Statements
4.4. Loop Statements
4.4.1. while and until Statements4.4.2. for Loops4.4.3. foreach Loops4.4.4. Loop Control
4.5. Bare Blocks
4.5.1. Case Structures
4.6. goto
4.7. Global Declarations
4.8. Scoped Declarations
4.8.1. Scoped Variable Declarations4.8.2. Lexically Scoped Variables: my4.8.3. Lexically Scoped Global Declarations: our4.8.4. Dynamically Scoped Variables: local
4.9. Pragmas
4.9.1. Controlling Warnings4.9.2. Controlling the Use of Globals
5. Pattern Matching
5.1. The Regular Expression Bestiary
5.2. Pattern-Matching Operators
5.2.1. Pattern Modifiers5.2.2. The m// Operator (Matching)5.2.3. The s/// Operator (Substitution)5.2.3.1. Modifying strings en passant5.2.3.2. When a global substitution just isn't global enough5.2.4. The tr/// Operator (Transliteration)
5.3. Metacharacters and Metasymbols
5.3.1. Metasymbol Tables5.3.2. Specific Characters5.3.3. Wildcard Metasymbols
5.4. Character Classes
5.4.1. Custom Character Classes5.4.2. Classic Perl Character Class Shortcuts5.4.3. Unicode Properties5.4.3.1. Perl's Unicode properties5.4.3.2. Standard Unicode properties5.4.3.3. Unicode block properties5.4.3.4. Defining your own character properties5.4.4. POSIX-Style Character Classes
5.5. Quantifiers
5.6. Positions
5.6.1. Beginnings: The \A and ^ Assertions5.6.2. Endings: The \z, \Z, and $ Assertions5.6.3. Boundaries: The \b and \B Assertions5.6.4. Progressive Matching5.6.5. Where You Left Off: The \G Assertion
5.7. Capturing and Clustering
5.7.1. Capturing5.7.2. Clustering5.7.3. Cloistered Pattern Modifiers
5.8. Alternation
5.9. Staying in Control
5.9.1. Letting Perl Do the Work5.9.2. Variable Interpolation5.9.2.1. When backslashes happen5.9.2.2. The qr// quote regex operator5.9.3. The Regex Compiler5.9.4. The Little Engine That /Could(n't)?/
5.10. Fancy Patterns
5.10.1. Lookaround Assertions5.10.2. Nonbacktracking Subpatterns5.10.3. Programmatic Patterns5.10.3.1. Generated patterns5.10.3.2. Substitution evaluations5.10.3.3. Match-time code evaluation5.10.3.4. Match-time pattern interpolation5.10.3.5. Conditional interpolation5.10.4. Defining Your Own Assertions
6. Subroutines
6.1. Syntax
6.2. Semantics
6.2.1. Tricks with Parameter Lists6.2.2. Error Indications6.2.3. Scoping Issues
6.3. Passing References
6.4. Prototypes
6.4.1. Inlining Constant Functions6.4.2. Care with Prototypes
6.5. Subroutine Attributes
6.5.1. The locked and method Attributes6.5.2. The lvalue Attribute
7. Formats
7.1. Format Variables
7.2. Footers
7.2.1. Accessing Formatting Internals
8. References
8.1. What Is a Reference?
8.2. Creating References
8.2.1. The Backslash Operator8.2.2. Anonymous Data8.2.2.1. The anonymous array composer8.2.2.2. The anonymous hash composer8.2.2.3. The anonymous subroutine composer8.2.3. Object Constructors8.2.4. Handle References8.2.5. Symbol Table References8.2.6. Implicit Creation of References
8.3. Using Hard References
8.3.1. Using a Variable as a Variable Name8.3.2. Using a BLOCK as a Variable Name8.3.3. Using the Arrow Operator8.3.4. Using Object Methods8.3.5. Pseudohashes8.3.6. Other Tricks You Can Do with Hard References8.3.7. Closures8.3.7.1. Closures as function templates8.3.7.2. Nested subroutines
8.4. Symbolic References
8.5. Braces, Brackets, and Quoting
8.5.1. References Don't Work as Hash Keys8.5.2. Garbage Collection, Circular References, and Weak References
9. Data Structures
9.1. Arrays of Arrays9.1.1. Creating and Accessing a Two-Dimensional Array9.1.2. Growing Your Own9.1.3. Access and Printing9.1.4. Slices9.1.5. Common Mistakes
9.2. Hashes of Arrays
9.2.1. Composition of a Hash of Arrays9.2.2. Generation of a Hash of Arrays9.2.3. Access and Printing of a Hash of Arrays
9.3. Arrays of Hashes
9.3.1. Composition of an Array of Hashes9.3.2. Generation of an Array of Hashes9.3.3. Access and Printing of an Array of Hashes
9.4. Hashes of Hashes
9.4.1. Composition of a Hash of Hashes9.4.2. Generation of a Hash of Hashes9.4.3. Access and Printing of a Hash of Hashes
9.5. Hashes of Functions
9.6. More Elaborate Records
9.6.1. Composition, Access, and Printing of More Elaborate Records9.6.2. Composition, Access, and Printing of Even More Elaborate Records9.6.3. Generation of a Hash of Complex Records
9.7. Saving Data Structures
10. Packages
10.1. Symbol Tables
10.2. Autoloading
11. Modules
11.1. Using Modules
11.2. Creating Modules
11.2.1. Module Privacy and the Exporter11.2.1.1. Exporting without using Exporter's import method11.2.1.2. Version checking11.2.1.3. Managing unknown symbols11.2.1.4. Tag-handling utility functions
11.3. Overriding Built-in Functions
12. Objects
12.1. Brief Refresher on Object-Oriented Lingo
12.2. Perl's Object System
12.3. Method Invocation
12.3.1. Method Invocation Using the Arrow Operator12.3.2. Method Invocation Using Indirect Objects12.3.3. Syntactic Snafus with Indirect Objects12.3.4. Package-Quoted Classes
12.4. Object Construction
12.4.1. Inheritable Constructors12.4.2. Initializers
12.5. Class Inheritance
12.5.1. Inheritance Through @ISA12.5.2. Accessing Overridden Methods12.5.3. UNIVERSAL: The Ultimate Ancestor Class12.5.4. Method Autoloading12.5.5. Private Methods
12.6. Instance Destructors
12.6.1. Garbage Collection with DESTROY Methods
12.7. Managing Instance Data
12.7.1. Field Declarations with use fields12.7.2. Generating Classes with Class::Struct12.7.3. Generating Accessors with Autoloading12.7.4. Generating Accessors with Closures12.7.5. Using Closures for Private Objects12.7.6. New Tricks
12.8. Managing Class Data
12.9. Summary
13. Overloading
13.1. The overload Pragma
13.2. Overload Handlers
13.3. Overloadable Operators
13.4. The Copy Constructor (=)
13.5. When an Overload Handler Is Missing (nomethod and fallback)
13.6. Overloading Constants
13.7. Public Overload Functions
13.8. Inheritance and Overloading
13.9. Run-Time Overloading
13.10. Overloading Diagnostics
14. Tied Variables
14.1. Tying Scalars14.1.1. Scalar-Tying Methods14.1.2. Magical Counter Variables14.1.3. Magically Banishing $_
14.2. Tying Arrays
14.2.1. Array-Tying Methods14.2.2. Notational Convenience
14.3. Tying Hashes
14.3.1. Hash-Tying Methods
14.4. Tying Filehandles
14.4.1. Filehandle-Tying Methods14.4.2. Creative Filehandles
14.5. A Subtle Untying Trap
14.6. Tie Modules on CPAN
III. Perl as Technology
15. Unicode
15.1. Building Character
15.2. Effects of Character Semantics
15.3. Caveats
16. Interprocess Communication
16.1. Signals16.1.1. Signaling Process Groups16.1.2. Reaping Zombies16.1.3. Timing Out Slow Operations16.1.4. Blocking Signals
16.2. Files
16.2.1. File Locking16.2.2. Passing Filehandles
16.3. Pipes
16.3.1. Anonymous Pipes16.3.2. Talking to Yourself16.3.3. Bidirectional Communication16.3.4. Named Pipes
16.4. System V IPC
16.5. Sockets
16.5.1. Networking Clients16.5.2. Networking Servers16.5.3. Message Passing
17. Threads
17.1. The Process Model
17.2. The Thread Model
17.2.1. The Thread Module17.2.1.1. Thread creation17.2.1.2. Thread destruction17.2.1.3. Catching exceptions from join17.2.1.4. The detach method17.2.1.5. Identifying threads17.2.1.6. Listing current threads17.2.1.7. Yielding the processor17.2.2. Data Access17.2.2.1. Synchronizing access with lock17.2.2.2. Deadlock17.2.2.3. Locking subroutines17.2.2.4. The locked attribute17.2.2.5. Locking methods17.2.2.6. Condition variables17.2.3. Other Thread Modules17.2.3.1. Queues17.2.3.2. Semaphores17.2.3.3. Other standard threading modules
18. Compiling
18.1. The Life Cycle of a Perl Program
18.2. Compiling Your Code
18.3. Executing Your Code
18.4. Compiler Backends
18.5. Code Generators
18.5.1. The Bytecode Generator18.5.2. The C Code Generators
18.6. Code Development Tools
18.7. Avant-Garde Compiler, Retro Interpreter
19. The Command-Line Interface
19.1. Command Processing19.1.1. #! and Quoting on Non-Unix Systems19.1.2. Location of Perl19.1.3. Switches
19.2. Environment Variables
20. The Perl Debugger
20.1. Using the Debugger
20.2. Debugger Commands
20.2.1. Stepping and Running20.2.2. Breakpoints20.2.3. Tracing20.2.4. Display20.2.5. Locating Code20.2.6. Actions and Command Execution20.2.7. Miscellaneous Commands
20.3. Debugger Customization
20.3.1. Editor Support for Debugging20.3.2. Customizing with Init Files20.3.3. Debugger Options
20.4. Unattended Execution
20.5. Debugger Support
20.5.1. Writing Your Own Debugger
20.6. The Perl Profiler
21. Internals and Externals
21.1. How Perl Works
21.2. Internal Data Types
21.3. Extending Perl (Using C from Perl)
21.3.1. XS and XSUBs21.3.2. Creating Extensions21.3.3. XSUB Input and Output21.3.4. Using Functions from an External C Library
21.4. Embedding Perl (Using Perl from C)
21.4.1. Compiling Embedded Programs21.4.2. Adding a Perl Interpreter to Your C Program21.4.3. Calling a Perl Subroutine from C21.4.4. Evaluating a Perl Statement from C21.4.5. Fiddling with the Perl Stack from C
21.5. The Moral of the Story
IV. Perl as Culture
22. CPAN
22.1. The CPAN modules Directory
22.2. Using CPAN Modules
22.2.1. Decompressing and Unpacking CPAN Modules22.2.2. Building CPAN Modules22.2.3. Installing CPAN Modules into the Perl Library
22.3. Creating CPAN Modules
22.3.1. Internal Testing22.3.2. External Testing
23. Security
23.1. Handling Insecure Data23.1.1. Detecting and Laundering Tainted Data23.1.2. Cleaning Up Your Environment23.1.3. Accessing Commands and Files Under Reduced Privileges
23.2. Handling Timing Glitches
23.2.1. Unix Kernel Security Bugs23.2.2. Handling Race Conditions23.2.3. Temporary Files
23.3. Handling Insecure Code
23.3.1. Safe Compartments23.3.1.1. Restricting namespace access23.3.1.2. Restricting operator access23.3.1.3. Safe examples23.3.2. Code Masquerading as Data
24. Common Practices
24.1. Common Goofs for Novices24.1.1. Universal Blunders24.1.2. Frequently Ignored Advice24.1.3. C Traps24.1.4. Shell Traps24.1.5. Previous Perl Traps
24.2. Efficiency
24.2.1. Time Efficiency24.2.2. Space Efficiency24.2.3. Programmer Efficiency24.2.4. Maintainer Efficiency24.2.5. Porter Efficiency24.2.6. User Efficiency
24.3. Programming with Style
24.4. Fluent Perl
24.5. Program Generation
24.5.1. Generating Other Languages in Perl24.5.2. Generating Perl in Other Languages24.5.3. Source Filters
25. Portable Perl
25.1. Newlines
25.2. Endianness and Number Width
25.3. Files and Filesystems
25.4. System Interaction
25.5. Interprocess Communication (IPC)
25.6. External Subroutines (XS)
25.7. Standard Modules
25.8. Dates and Times
25.9. Internationalization
25.10. Style
26. Plain Old Documentation
26.1. Pod in a Nutshell26.1.1. Verbatim Paragraphs26.1.2. Pod Directives26.1.3. Pod Sequences
26.2. Pod Translators and Modules
26.3. Writing Your Own Pod Tools
26.4. Pod Pitfalls
26.5. Documenting Your Perl Programs
27. Perl Culture
27.1. History Made Practical
27.2. Perl Poetry
V. Reference Material
28. Special Names
28.1. Special Names Grouped by Type28.1.1. Regular Expression Special Variables28.1.2. Per-Filehandle Variables28.1.3. Per-Package Special Variables28.1.4. Program-wide Special Variables28.1.5. Per-Package Special Filehandles28.1.6. Per-Package Special Functions
28.2. Special Variables in Alphabetical Order
29. Functions
29.1. Perl Functions by Category
29.2. Perl Functions in Alphabetical Order
29.2.1. abs29.2.2. accept29.2.3. alarm29.2.4. atan229.2.5. bind29.2.6. binmode29.2.7. bless29.2.8. caller29.2.9. chdir29.2.10. chmod29.2.11. chomp29.2.12. chop29.2.13. chown29.2.14. chr29.2.15. chroot29.2.16. close29.2.17. closedir29.2.18. connect29.2.19. cos29.2.20. crypt29.2.21. dbmclose29.2.22. dbmopen29.2.23. defined29.2.24. delete29.2.25. die29.2.26. do (block)29.2.27. do (file)29.2.28. do (subroutine)29.2.29. dump29.2.30. each29.2.31. eof29.2.32. eval29.2.33. exec29.2.34. exists29.2.35. exit29.2.36. exp29.2.37. fcntl29.2.38. fileno29.2.39. flock29.2.40. fork29.2.41. format29.2.42. formline29.2.43. getc29.2.44. getgrent29.2.45. getgrgid29.2.46. getgrnam29.2.47. gethostbyaddr29.2.48. gethostbyname29.2.49. gethostent29.2.50. getlogin29.2.51. getnetbyaddr29.2.52. getnetbyname29.2.53. getnetent29.2.54. getpeername29.2.55. getpgrp29.2.56. getppid29.2.57. getpriority29.2.58. getprotobyname29.2.59. getprotobynumber29.2.60. getprotoent29.2.61. getpwent29.2.62. getpwnam29.2.63. getpwuid29.2.64. getservbyname29.2.65. getservbyport29.2.66. getservent29.2.67. getsockname29.2.68. getsockopt29.2.69. glob29.2.70. gmtime29.2.71. goto29.2.72. grep29.2.73. hex29.2.74. import29.2.75. index29.2.76. int29.2.77. ioctl29.2.78. join29.2.79. keys29.2.80. kill29.2.81. last29.2.82. lc29.2.83. lcfirst29.2.84. length29.2.85. link29.2.86. listen29.2.87. local29.2.88. localtime29.2.89. lock29.2.90. log29.2.91. lstat29.2.92. m//29.2.93. map29.2.94. mkdir29.2.95. msgctl29.2.96. msgget29.2.97. msgrcv29.2.98. msgsnd29.2.99. my29.2.100. new29.2.101. next29.2.102. no29.2.103. oct29.2.104. open29.2.105. opendir29.2.106. ord29.2.107. our29.2.108. pack29.2.109. package29.2.110. pipe29.2.111. pop29.2.112. pos29.2.113. print29.2.114. printf29.2.115. prototype29.2.116. push29.2.117. q/STRING/29.2.118. quotemeta29.2.119. rand29.2.120. read29.2.121. readdir29.2.122. readline29.2.123. readlink29.2.124. readpipe29.2.125. recv29.2.126. redo29.2.127. ref29.2.128. rename29.2.129. require29.2.130. reset29.2.131. return29.2.132. reverse29.2.133. rewinddir29.2.134. rindex29.2.135. rmdir29.2.136. s///29.2.137. scalar29.2.138. seek29.2.139. seekdir29.2.140. select (output filehandle)29.2.141. select (ready file descriptors)29.2.142. semctl29.2.143. semget29.2.144. semop29.2.145. send29.2.146. setpgrp29.2.147. setpriority29.2.148. setsockopt29.2.149. shift29.2.150. shmctl29.2.151. shmget29.2.152. shmread29.2.153. shmwrite29.2.154. shutdown29.2.155. sin29.2.156. sleep29.2.157. socket29.2.158. socketpair29.2.159. sort29.2.160. splice29.2.161. split29.2.162. sprintf29.2.163. sqrt29.2.164. srand29.2.165. stat29.2.166. study29.2.167. sub29.2.168. substr29.2.169. symlink29.2.170. syscall29.2.171. sysopen29.2.172. sysread29.2.173. sysseek29.2.174. system29.2.175. syswrite29.2.176. tell29.2.177. telldir29.2.178. tie29.2.179. tied29.2.180. time29.2.181. times29.2.182. tr///29.2.183. truncate29.2.184. uc29.2.185. ucfirst29.2.186. umask29.2.187. undef29.2.188. unlink29.2.189. unpack29.2.190. unshift29.2.191. untie29.2.192. use29.2.193. utime29.2.194. values29.2.195. vec29.2.196. wait29.2.197. waitpid29.2.198. wantarray29.2.199. warn29.2.200. write29.2.201. //
30. The Standard Perl Library
30.1. Library Science
30.2. A Tour of the Perl Library
31. Pragmatic Modules
31.1. use attributes
31.2. use autouse
31.3. use base
31.4. use blib
31.5. use bytes
31.6. use charnames
31.7. use constant
31.7.1. Restrictions on use constant
31.8. use diagnostics
31.9. use fields
31.10. use filetest
31.10.1. use filetest 'access'
31.11. use integer
31.12. use less
31.13. use lib
31.14. use locale
31.15. use open
31.16. use overload
31.17. use re
31.18. use sigtrap
31.18.1. Signal Handlers31.18.2. Predefined Signal Lists31.18.3. Other Arguments to sigtrap31.18.4. Examples of sigtrap
31.19. use strict
31.19.1. strict 'refs'31.19.2. strict 'vars'31.19.3. strict 'subs'
31.20. use subs
31.21. use vars
31.22. use warnings
32. Standard Modules
32.1. Listings by Type32.1.1. Data Types32.1.2. String Processing, Language Text Processing, Parsing, and Searching32.1.3. Option, Argument, Parameter, and Configuration File Processing32.1.4. Filenames, Filesystems, and File Locking32.1.5. Filehandle, Directory Handle, and Stream I/O Utilities32.1.6. Internationalization and Locale32.1.7. Operating System Interfaces32.1.8. Networking and Interprocess Communication32.1.9. World Wide Web32.1.10. DBM Interfaces32.1.11. User Interfaces32.1.12. Authentication, Security, and Encryption32.1.13. Perl Language Extensions and Internals32.1.14. Convenient Classes32.1.15. Warnings and Exceptions32.1.16. Documentation Support32.1.17. Module Installation Support32.1.18. Development Support32.1.19. Perl Compiler and Code Generator32.1.20. Microsoft-Related Modules
32.2. Benchmark
32.3. Carp
32.4. CGI
32.5. CGI::Carp
32.6. Class::Struct
32.7. Config
32.8. CPAN
32.9. Cwd
32.10. Data::Dumper
32.11. DB_File
32.12. Dumpvalue
32.13. English
32.14. Errno
32.15. Exporter
32.16. Fatal
32.17. Fcntl
32.18. File::Basename
32.19. File::Compare
32.20. File::Copy
32.21. File::Find
32.22. File::Glob
32.23. File::Spec
32.24. File::stat
32.25. File::Temp
32.26. FileHandle
32.27. Getopt::Long
32.28. Getopt::Std
32.29. IO::Socket
32.30. IPC::Open2
32.31. IPC::Open3
32.32. Math::BigInt
32.33. Math::Complex
32.34. Math::Trig
32.35. Net::hostent
32.36. POSIX
32.37. Safe
32.38. Socket
32.39. Symbol
32.40. Sys::Hostname
32.41. Sys::Syslog
32.42. Term::Cap
32.43. Text::Wrap
32.44. Time::Local
32.45. Time::localtime
32.46. User::grent
32.47. User::pwent
33. Diagnostic Messages
Glossary
Index
About the Authors
Colophon

Content preview from Programming Perl, 3rd Edition

Relational Operators

Perl has two classes of relational operators. One class operates on numeric values, the other on string values, as shown in Table 3.5.

Table 3-5. Relational Operators

Numeric	String	Meaning
`>`	`gt`	Greater than
`>=`	`ge`	Greater than or equal to
`<`	`lt`	Less than
`<=`	`le`	Less than or equal to

These operators return 1 for true and "" for false. Note that relational operators are nonassociating, which means that $a < $b < $c is a syntax error.

In the absence of locale declarations, string comparisons are based on the ASCII/Unicode collating sequences, and, unlike in some computer languages, trailing spaces count in the comparison. With a locale declaration, the collation order specified by the locale is used. (Locale-based collation mechanisms may or may not interact well with the Unicode collation mechanisms currently in development.)

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Programming Perl, 3rd Edition

by Larry Wall, Tom Christiansen, Jon Orwant

Relational Operators

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