Table of Contents for
sed & awk, 2nd Edition

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition sed & awk, 2nd Edition by Arnold Robbins Published by O'Reilly Media, Inc., 1997
  1. sed & awk, 2nd Edition
  2. Cover
  3. sed & awk, 2nd Edition
  4. A Note Regarding Supplemental Files
  5. Dedication
  6. Preface
  7. Scope of This Handbook
  8. Availability of sed and awk
  9. Obtaining Example Source Code
  10. Conventions Used in This Handbook
  11. About the Second Edition
  12. Acknowledgments from the First Edition
  13. Comments and Questions
  14. 1. Power Tools for Editing
  15. 1.1. May You Solve Interesting Problems
  16. 1.2. A Stream Editor
  17. 1.3. A Pattern-Matching Programming Language
  18. 1.4. Four Hurdles to Mastering sed and awk
  19. 2. Understanding Basic Operations
  20. 2.1. Awk, by Sed and Grep, out of Ed
  21. 2.2. Command-Line Syntax
  22. 2.3. Using sed
  23. 2.4. Using awk
  24. 2.5. Using sed and awk Together
  25. 3. Understanding Regular Expression Syntax
  26. 3.1. That’s an Expression
  27. 3.2. A Line-Up of Characters
  28. 3.3. I Never Metacharacter I Didn’t Like
  29. 4. Writing sed Scripts
  30. 4.1. Applying Commands in a Script
  31. 4.2. A Global Perspective on Addressing
  32. 4.3. Testing and Saving Output
  33. 4.4. Four Types of sed Scripts
  34. 4.5. Getting to the PromiSed Land
  35. 5. Basic sed Commands
  36. 5.1. About the Syntax of sed Commands
  37. 5.2. Comment
  38. 5.3. Substitution
  39. 5.4. Delete
  40. 5.5. Append, Insert, and Change
  41. 5.6. List
  42. 5.7. Transform
  43. 5.8. Print
  44. 5.9. Print Line Number
  45. 5.10. Next
  46. 5.11. Reading and Writing Files
  47. 5.12. Quit
  48. 6. Advanced sed Commands
  49. 6.1. Multiline Pattern Space
  50. 6.2. A Case for Study
  51. 6.3. Hold That Line
  52. 6.4. Advanced Flow Control Commands
  53. 6.5. To Join a Phrase
  54. 7. Writing Scripts for awk
  55. 7.1. Playing the Game
  56. 7.2. Hello, World
  57. 7.3. Awk’s Programming Model
  58. 7.4. Pattern Matching
  59. 7.5. Records and Fields
  60. 7.6. Expressions
  61. 7.7. System Variables
  62. 7.8. Relational and Boolean Operators
  63. 7.9. Formatted Printing
  64. 7.10. Passing Parameters Into a Script
  65. 7.11. Information Retrieval
  66. 8. Conditionals, Loops, and Arrays
  67. 8.1. Conditional Statements
  68. 8.2. Looping
  69. 8.3. Other Statements That Affect Flow Control
  70. 8.4. Arrays
  71. 8.5. An Acronym Processor
  72. 8.6. System Variables That Are Arrays
  73. 9. Functions
  74. 9.1. Arithmetic Functions
  75. 9.2. String Functions
  76. 9.3. Writing Your Own Functions
  77. 10. The Bottom Drawer
  78. 10.1. The getline Function
  79. 10.2. The close( ) Function
  80. 10.3. The system( ) Function
  81. 10.4. A Menu-Based Command Generator
  82. 10.5. Directing Output to Files and Pipes
  83. 10.6. Generating Columnar Reports
  84. 10.7. Debugging
  85. 10.8. Limitations
  86. 10.9. Invoking awk Using the #! Syntax
  87. 11. A Flock of awks
  88. 11.1. Original awk
  89. 11.2. Freely Available awks
  90. 11.3. Commercial awks
  91. 11.4. Epilogue
  92. 12. Full-Featured Applications
  93. 12.1. An Interactive Spelling Checker
  94. 12.2. Generating a Formatted Index
  95. 12.3. Spare Details of the masterindex Program
  96. 13. A Miscellany of Scripts
  97. 13.1. uutot.awk—Report UUCP Statistics
  98. 13.2. phonebill—Track Phone Usage
  99. 13.3. combine—Extract Multipart uuencoded Binaries
  100. 13.4. mailavg—Check Size of Mailboxes
  101. 13.5. adj—Adjust Lines for Text Files
  102. 13.6. readsource—Format Program Source Files for troff
  103. 13.7. gent—Get a termcap Entry
  104. 13.8. plpr—lpr Preprocessor
  105. 13.9. transpose—Perform a Matrix Transposition
  106. 13.10. m1—Simple Macro Processor
  107. A. Quick Reference for sed
  108. A.1. Command-Line Syntax
  109. A.2. Syntax of sed Commands
  110. A.3. Command Summary for sed
  111. B. Quick Reference for awk
  112. B.1. Command-Line Syntax
  113. B.2. Language Summary for awk
  114. B.3. Command Summary for awk
  115. C. Supplement for Chapter 12
  116. C.1. Full Listing of spellcheck.awk
  117. C.2. Listing of masterindex Shell Script
  118. C.3. Documentation for masterindex
  119. masterindex
  120. C.3.1. Background Details
  121. C.3.2. Coding Index Entries
  122. C.3.3. Output Format
  123. C.3.4. Compiling a Master Index
  124. Index
  125. About the Authors
  126. Colophon
  127. Copyright

Chapter 4. Writing sed Scripts

To use sed, you write a script that contains a series of editing actions and then you run the script on an input file. Sed allows you to take what would be a hands-on procedure in an editor such as vi and transform it into a look-no-hands procedure that is executed from a script.

When performing edits manually, you come to trust the cause-and-effect relationship of entering an editing command and seeing the immediate result. There is usually an “undo” command that allows you to reverse the effect of a command and return the text file to its previous state. Once you learn an interactive text editor, you experience the feeling of making changes in a safe and controlled manner, one step at a time.

Most people new to sed will feel there is greater risk in writing a script to perform a series of edits than in making those changes manually. The fear is that by automating the task, something will happen that cannot be reversed. The object of learning sed is to understand it well enough to see that your results are predictable. In other words, you come to understand the cause-and-effect relationship between your editing script and the output that you get.

This requires using sed in a controlled, methodical way. In writing a script, you should follow these steps:

  1. Think through what you want to do before you do it.

  2. Describe, unambiguously, a procedure to do it.

  3. Test the procedure repeatedly before committing to any final changes.

These steps are simply a restatement of the same process we described for writing regular expressions in Chapter 3. They describe a methodology for writing programs of any kind. The best way to see if your script works is to run tests on different input samples and observe the results.

With practice, you can come to rely upon your sed scripts working just as you want them to. (There is something analogous in the management of one’s own time, learning to trust that certain tasks can be delegated to others. You begin testing people on small tasks, and if they succeed, you give them larger tasks.)

This chapter, then, is about making you comfortable writing scripts that do your editing work for you. This involves understanding three basic principles of how sed works:

  • All editing commands in a script are applied in order to each line of input.

  • Commands are applied to all lines (globally) unless line addressing restricts the lines affected by editing commands.

  • The original input file is unchanged; the editing commands modify a copy of original input line and the copy is sent to standard output.

After covering these basic principles, we’ll look at four types of scripts that demonstrate different sed applications. These scripts provide the basic models for the scripts that you will write. Although there are a number of commands available for use in sed, the scripts in this chapter purposely use only a few commands. Nonetheless, you may be surprised at how much you can do with so few. (Chapter 5, and Chapter 6, present the basic and advanced sed commands, respectively.) The idea is to concentrate from the outset on understanding how a script works and how to use a script before exploring all the commands that can be used in scripts.