Effective Perl Programming

Joseph N. Hall has programmed for a living since 1984, taught his first computer class at age fourteen, and has worked with Perl since 1993. Joshua A. McAdams, a programmer at Google, is the voice of Perlcast. He has hosted two Perl conferences, conducts meetings for Chicago Perl Mongers, has spoken about Perl at events worldwide, and is a CPAN author. brian d foy is coauthor of Learning Perl, Fifth Edition (O’Reilly Media, 2008), and Intermediate Perl (O’Reilly Media, 2006), and author of Mastering Perl (O’Reilly Media, 2007). He established the first Perl user group, the New York Perl Mongers; publishes The Perl Review; maintains parts of the core Perl documentation; and has more than ten years of Perl training experience.

Foreword xi Preface xiii

Acknowledgments xvii

About the Authors xix

 

Introduction 1

 

Chapter 1: The Basics of Perl 9

Item 1. Find the documentation for Perl and its modules. 9

Item 2. Enable new Perl features when you need them. 12

Item 3. Enable strictures to promote better coding. 14

Item 4. Understand what sigils are telling you. 17

Item 5. Know your variable namespaces. 19

Item 6. Know the difference between string and numeric comparisons. 21

Item 7. Know which values are false and test them accordingly. 23

Item 8. Understand conversions between strings and numbers. 27

Item 9. Know the difference between lists and arrays. 31

Item 10. Don’t assign undef when you want an empty array. 34

Item 11. Avoid a slice when you want an element. 37

Item 12. Understand context and how it affects operations. 41

Item 13. Use arrays or hashes to group data. 45

Item 14. Handle big numbers with bignum. 47

 

Chapter 2: Idiomatic Perl 51

Item 15. Use $_ for elegance and brevity. 53

Item 16. Know Perl’s other default arguments. 56

Item 17. Know common shorthand and syntax quirks. 60

Item 18. Avoid excessive punctuation. 66

Item 19. Format lists for easy maintenance. 68

Item 20. Use foreach, map, and grep as appropriate. 70

Item 21. Know the different ways to quote strings. 73

Item 22. Learn the myriad ways of sorting. 77

Item 23. Make work easier with smart matching. 84

Item 24. Use given-when to make a switch statement. 86

Item 25. Use do {} to create inline subroutines. 90

Item 26. Use List::Util and List::MoreUtils for easy list manipulation. 92

Item 27. Use autodie to simplify error handling. 96

 

Chapter 3: Regular Expressions 99

Item 28. Know the precedence of regular expression operators. 99

Item 29. Use regular expression captures. 103

Item 30. Use more precise whitespace character classes. 110

Item 31. Use named captures to label matches. 114

Item 32. Use noncapturing parentheses when you need only grouping. 116

Item 33. Watch out for the match variables. 117

Item 34. Avoid greed when parsimony is best. 119

Item 35. Use zero-width assertions to match positions in a string. 121

Item 36. Avoid using regular expressions for simple string operations. 125

Item 37. Make regular expressions readable. 129

Item 38. Avoid unnecessary backtracking. 132

Item 39. Compile regexes only once. 137

Item 40. Pre-compile regular expressions. 138

Item 41. Benchmark your regular expressions. 139

Item 42. Don’t reinvent the regex. 142

 

Chapter 4: Subroutines 145

Item 43. Understand the difference between my and local. 145

Item 44. Avoid using @_ directly unless you have to. 154

Item 45. Use wantarray to write subroutines returning lists. 157

Item 46. Pass references instead of copies. 160

Item 47. Use hashes to pass named parameters. 164

Item 48. Use prototypes to get special argument parsing. 168

Item 49. Create closures to lock in data. 171

Item 50. Create new subroutines with subroutines. 176

 

Chapter 5: Files and Filehandles 179

Item 51. Don’t ignore the file test operators. 179

Item 52. Always use the three-argument open. 182

Item 53. Consider different ways of reading from a stream. 183

Item 54. Open filehandles to and from strings. 186

Item 55. Make flexible output. 189

Item 56. Use File::Spec or Path::Class to work with paths. 192

Item 57. Leave most of the data on disk to save memory. 195

 

Chapter 6: References 201

Item 58. Understand references and reference syntax. 201

Item 59. Compare reference types to prototypes. 209

Item 60. Create arrays of arrays with references. 211

Item 61. Don’t confuse anonymous arrays with list literals. 214

Item 62. Build C-style structs with anonymous hashes. 216

Item 63. Be careful with circular data structures. 218

Item 64. Use map and grep to manipulate complex data structures. 221

 

Chapter 7: CPAN 227

Item 65. Install CPAN modules without admin privileges. 228

Item 66. Carry a CPAN with you. 231

Item 67. Mitigate the risk of public code. 235

Item 68. Research modules before you install them. 239

Item 69. Ensure that Perl can find your modules. 242

Item 70. Contribute to CPAN. 246

Item 71. Know the commonly used modules. 250

 

Chapter 8: Unicode 253

Item 72. Use Unicode in your source code. 254

Item 73. Tell Perl which encoding to use. 257

Item 74. Specify Unicode characters by code point or name. 258

Item 75. Convert octet strings to character strings. 261

Item 76. Match Unicode characters and properties. 265

Item 77. Work with graphemes instead of characters. 269

Item 78. Be careful with Unicode in your databases. 272

 

Chapter 9: Distributions 275

Item 79. Use Module::Build as your distribution builder. 275

Item 80. Don’t start distributions by hand. 278

Item 81. Choose a good module name. 283

Item 82. Embed your documentation with Pod. 287

Item 83. Limit your distributions to the right platforms. 292

Item 84. Check your Pod. 295

Item 85. Inline code for other languages. 298

Item 86. Use XS for low-level interfaces and speed. 301

 

Chapter 10: Testing 307

Item 87. Use prove for flexible test runs. 308

Item 88. Run tests only when they make sense. 311

Item 89. Use dependency injection to avoid special test logic. 314

Item 90. Don’t require more than you need to use in your methods. 317

Item 91. Write programs as modulinos for easy testing. 320

Item 92. Mock objects and interfaces to focus tests. 324

Item 93. Use SQLite to create test databases. 330

Item 94. Use Test::Class for more structured testing. 332

Item 95. Start testing at the beginning of your project. 335

Item 96. Measure your test coverage. 342

Item 97. Use CPAN Testers as your QA team. 346

Item 98. Set up a continuous build system. 348

 

Chapter 11: Warnings 357

Item 99. Enable warnings to let Perl spot suspicious code. 358

Item 100. Use lexical warnings to selectively turn on or off complaints. 361

Item 101. Use die to generate exceptions. 364

Item 102. Use Carp to get stack traces. 366

Item 103. Handle exceptions properly. 370

Item 104. Track dangerous data with taint checking. 372

Item 105. Start with taint warnings for legacy code. 375

 

Chapter 12: Databases 377

Item 106. Prepare your SQL statements to reuse work and save time. 377

Item 107. Use SQL placeholders for automatic value quoting. 382

Item 108. Bind return columns for faster access to data. 384

Item 109. Reuse database connections. 386

 

Chapter 13: Miscellany 391

Item 110. Compile and install your own perls. 391

Item 111. Use Perl::Tidy to beautify code. 394

Item 112. Use Perl Critic. 398

Item 113. Use Log::Log4perl to record your program’s state. 403

Item 114. Know when arrays are modified in a loop. 410

Item 115. Don’t use regular expressions for comma-separated values. 412

Item 116. Use unpack to process columnar data. 414

Item 117. Use pack and unpack for data munging. 416

Item 118. Access the symbol table with typeglobs. 423

Item 119. Initialize with BEGIN; finish with END. 425

Item 120. Use Perl one-liners to create mini programs. 428

 

Appendix A: Perl Resources 435

 

Appendix B: Map from First to Second Edition 439

Books 435

Websites 436

Blogs and Podcasts 437

Getting Help 437

 

Index 445