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

Command-Line Syntax

You invoke sed and awk in much the same way. The command-line syntax is:

command [options] script filename

Like almost all UNIX programs, sed and awk can take input from standard input and send the output to standard output. If a filename is specified, input is taken from that file. The output contains the processed information. Standard output is the display screen, and typically the output from these programs is directed there. It can also be sent to a file, using I/O redirection in the shell, but it must not go to the same file that supplies input to the program.

The options for each command are different. We will demonstrate many of these options in upcoming sections. (The complete list of command-line options for sed can be found in Appendix A; the complete list of options for awk is in Appendix B.)

The script specifies what instructions to perform. If specified on the command line, the script must be surrounded in single quotes if it contains a space or any characters that might be interpreted by the shell ($ and * for instance).

One option common to both sed and awk is the -f option that allows you to specify the name of a script file. As a script grows in size, it is convenient to place it in a file. Thus, you might invoke sed as follows:

sed -f scriptfile inputfile

Figure 2.1 shows the basic operation of sed and awk. Each program reads one input line at a time from the input file, makes a copy of the input line, and executes the instructions specified in the script on that copy. Thus, changes made to the input line do not affect the actual input file.

How sed and awk work
Figure 2.1. How sed and awk work

Scripting

A script is where you tell the program what to do. At least one line of instruction is required. Short scripts can be specified on the command line; longer scripts are usually placed in a file where they can easily be revised and tested. In writing a script, keep in mind the sequence in which instructions will be executed and how each instruction changes the input line.

In sed and awk, each instruction has two parts: a pattern and a procedure. The pattern is a regular expression delimited with slashes (/). A procedure specifies one or more actions to be performed.

As each line of input is read, the program reads the first instruction in the script and checks the pattern against the current line. If there is no match, the procedure is ignored and the next instruction is read. If there is a match, then the action or actions specified in the procedure are followed. All of the instructions are read, not just the first instruction that matches the input line.

When all the applicable instructions have been interpreted and applied for a single line, sed outputs the line and repeats the cycle for each input line. Awk, on the other hand, does not automatically output the line; the instructions in your script control what is finally done with it.

The contents of a procedure are very different in sed and awk. In sed, the procedure consists of editing commands like those used in the line editor. Most commands consist of a single letter.

In awk, the procedure consists of programming statements and functions. A procedure must be surrounded by braces.

In the sections that follow, we’ll look at a few scripts that process a sample mailing list.

Sample Mailing List

In the upcoming sections, the examples use a sample file, named list. It contains a list of names and addresses, as shown below.

$ cat list
John Daggett, 341 King Road, Plymouth MA
Alice Ford, 22 East Broadway, Richmond VA
Orville Thomas, 11345 Oak Bridge Road, Tulsa OK
Terry Kalkas, 402 Lans Road, Beaver Falls PA
Eric Adams, 20 Post Road, Sudbury MA
Hubert Sims, 328A Brook Road, Roanoke VA
Amy Wilde, 334 Bayshore Pkwy, Mountain View CA
Sal Carpenter, 73 6th Street, Boston MA

If you like, create this file on your system or use a similar one of your own making. Because many of the examples in this chapter are short and interactive, you can enter them at your keyboard and verify the results.