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Exploring Expect

Cover of Exploring Expect by Don Libes Published by O'Reilly Media, Inc.
  1. Exploring Expect
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. A Note Regarding Supplemental Files
    3. Preface
      1. Expect—Why another tool?
      2. Tcl—A Little History
      3. Acknowledgments
      4. We’d Like to Hear From You
    4. How To Read This Book
      1. Notational Conventions
      2. Exercises
    5. 1. Intro—What Is Expect?
      1. Ouch, Those Programs Are Painful!
      2. A Very Brief Overview
      3. A First Script—dialback
      4. Total Automation
      5. Differing Behavior When Running Non-Interactively
      6. Partial Automation
      7. Dangerous, Unfriendly, Or Otherwise Unlikable User Interfaces
      8. Graphical Applications
      9. A Little More About Tcl
      10. Job Control
      11. Background Processes
      12. Using Expect With Other Programs
      13. Using Expect On UNIX
      14. Using Expect On Other Operating Systems
      15. Using Expect In Real Applications
      16. Using Expect In Commercial Applications—Legalese
      17. Obtaining Expect and the Examples
      18. Expect And Tcl Resources
      19. Exercises
    6. 2. Tcl—Introduction And Overview
      1. Everything Is A String
      2. Quoting Conventions
      3. Expressions
      4. Braces—Deferring Evaluation
      5. Control Structures
      6. More On Expressions
      7. Lists
      8. More Ways To Manipulate Strings
      9. Arrays
      10. Indirect References
      11. Handling Errors
      12. Evaluating Lists As Commands
      13. Passing By Reference
      14. Working With Files
      15. File I/O
      16. Executing UNIX Commands
      17. Environment Variables
      18. Handling Unknown Commands
      19. Libraries
      20. Is There More To Tcl?
      21. Exercises
    7. 3. Getting Started With Expect
      1. The send Command
      2. The expect Command
      3. Anchoring
      4. What Happens When Input Does Not Match
      5. Pattern-Action Pairs
      6. Example—Timed Reads In The Shell
      7. The spawn Command
      8. The interact Command
      9. Example—Anonymous ftp
      10. Exercises
    8. 4. Glob Patterns And Other Basics
      1. The * Wildcard
      2. More Glob Patterns
      3. Backslashes
      4. Handling Timeout
      5. Handling End Of File (eof)
      6. Hints On The spawn Command
      7. Back To Eof
      8. The close Command
      9. Programs That Ignore Eof
      10. The wait Command
      11. Exercises
    9. 5. Regular Expressions
      1. Regular Expressions—A Quick Start
      2. Identifying Regular Expressions And Glob Patterns
      3. Using Parentheses To Override Precedence
      4. Using Parentheses For Feedback
      5. More On The timed–read Script
      6. Pattern Matching Strategy
      7. Nested Parentheses
      8. Always Count Parentheses Even Inside Of Alternatives
      9. Example—The Return Value From A Remote Shell
      10. Matching Customized Prompts
      11. Example—A Smart Remote Login Script
      12. What Else Gets Stored In expect_out
      13. More On Anchoring
      14. Exercises
    10. 6. Patterns, Actions, And Limits
      1. Matching Anything But
      2. Really Complex Patterns
      3. Really Simple Patterns
      4. Matching One Line And Only One Line
      5. Tcl’s string match Command
      6. Tcl’s regexp Command
      7. Tcl’s regsub Command
      8. Ignoring Case
      9. All Those Other String Functions Are Handy, Too
      10. Actions That Affect Control Flow
      11. Example—rogue
      12. Character Graphics
      13. More Actions That Affect Control Flow
      14. Matching Multiple Times
      15. Recognizing Prompts (Yet Again)
      16. Speed Is On Your Side
      17. Controlling The Limits Of Pattern Matching Input
      18. The full_buffer Keyword
      19. Double Buffering
      20. Perpetual Buffering
      21. The Politics Of Patterns
      22. Expecting A Null Character
      23. Parity
      24. Length Limits
      25. Comments In expect Commands
      26. Restrictions On expect Arguments
      27. eval—Good, Bad, And Ugly
      28. Exercises
    11. 7. Debugging Patterns And Controlling Output
      1. Pattern Debugging
      2. Enabling Internal Diagnostics
      3. Logging Internal Diagnostics
      4. Disabling Normal Program Output
      5. The log_user Command
      6. Example—su2
      7. Recording All Expect Output
      8. Sending Messages To The Log
      9. About File Names
      10. Log And Diagnostic State
      11. Exercises
    12. 8. Handling A Process And A User
      1. The send_user Command
      2. The send_error Command
      3. The expect_user Command
      4. Dealing With Programs That Reprompt
      5. Dealing With Programs That Miss Input
      6. Sleeping
      7. Line Versus Character-Oriented And Other Terminal Modes
      8. Echoing
      9. Prompting For A Password On Behalf Of A Program
      10. Security And Insecurity
      11. Resetting The Terminal Upon Exit
      12. More On The stty Command
      13. The system Command
      14. Redirecting The Standard Input Or Output
      15. The expect_tty Command
      16. The send_tty Command
      17. Exercises
    13. 9. The Expect Program
      1. Expect—Just Another Program
      2. Invoking Scripts Without Saying “expect”
      3. Rewriting The #! Line
      4. The .exp Extension
      5. The—And Other Flags
      6. The —c Flag
      7. The -f Flag
      8. Writing The #! Line
      9. The −i Flag
      10. The -n And -N Flags
      11. The -d Flag
      12. The -D Flag
      13. The -b Flag
      14. The - Flag
      15. The interpreter Command
      16. Exercises
    14. 10. Handling Multiple Processes
      1. The spawn_id Variable
      2. Example—chess Versus chess
      3. Example—Automating The write Command
      4. How exp_continue Affects spawn_id
      5. The Value Of spawn_id Affects Many Commands
      6. Symbolic Spawn Ids
      7. Job Control
      8. Procedures Introduce New Scopes
      9. How Expect Writes Variables In Different Scopes
      10. Predefined Spawn Ids
      11. Exercises
    15. 11. Handling Multiple Processes Simultaneously
      1. Implicit Versus Explicit Spawn Ids
      2. Waiting From Multiple Processes Simultaneously
      3. Example—Answerback
      4. Which Pattern Goes With Which Spawn Id
      5. Which Spawn Id Matched
      6. Spawn Id Lists
      7. Example—Connecting Together Two Users To An Application
      8. Example—Timing All Commands
      9. Matching Any Spawn Id Already Listed
      10. The expect_before And expect_after Commands
      11. Indirect Spawn Ids
      12. Exercises
    16. 12. Send
      1. Implicit Versus Explicit Spawn Ids
      2. Sending To Multiple Processes
      3. Sending Without Echoing
      4. Sending To Programs In Cooked Mode
      5. Sending Slowly
      6. Sending Humanly
      7. Sending Nulls
      8. Sending Breaks
      9. Sending Strings That Look Like Flags
      10. Sending Character Graphics
      11. Comparing send To puts
      12. Exercises
    17. 13. Spawn
      1. The Search Path
      2. Philosophy--Processes Are Smart
      3. Treating Files As Spawned Processes
      4. Opening Ttys
      5. Bugs And Workarounds
      6. Process Pipelines And Ptys
      7. Automating xterm
      8. Checking For Errors From spawn
      9. spawn -noecho
      10. Example—unbuffer
      11. Obtaining Console Output
      12. Setting Pty Modes From spawn
      13. Hung Ptys
      14. Restrictions On Spawning Multiple Processes
      15. Getting The Process Id From A Spawn Id
      16. Using File I/O Commands On Spawned Processes
      17. Exercises
    18. 14. Signals
      1. Signals
      2. Signals In Spawned Processes
      3. Notes On Specific Signals
      4. When And Where Signals Are Evaluated
      5. Overriding The Original Return Value
      6. Using A Different Interpreter To Process Signals
      7. Exit Handling
      8. Exercises
    19. 15. Interact
      1. The interact Command
      2. Simple Patterns
      3. Exact Matching
      4. Matching Patterns From The Spawned Process
      5. Regular Expressions
      6. What Happens To Things That Do Not Match
      7. More Detail On Matching
      8. Echoing
      9. Avoiding Echoing
      10. Giving Feedback Without -echo
      11. Telling The User About New Features
      12. Sending Characters While Pattern Matching
      13. The continue And break Actions
      14. The return Action
      15. The Default Action
      16. Detecting End-Of-File
      17. Matching A Null Character
      18. Timing Out
      19. More On Terminal Modes (Or The -reset Flag)
      20. Example—Preventing Bad Commands
      21. Exercises
    20. 16. Interacting With Multiple Processes
      1. Connecting To A Process Other Than The Currently Spawned Process
      2. Connecting To A Process Instead Of The User
      3. Example—rz And sz Over rlogin
      4. Redirecting Input And Output
      5. Default Input And Output
      6. Controlling Multiple Processes—kibitz
      7. Combining Spawn Ids In A Single -input Or -output
      8. Which Spawn Id Matched
      9. Indirect Spawn Ids
      10. An Extended Example—xkibitz
      11. Exercises
    21. 17. Background Processing
      1. Putting Expect In The Background
      2. Running Expect Without A Controlling Terminal
      3. Disconnecting The Controlling Terminal
      4. The fork Command
      5. The disconnect Command
      6. Reconnecting
      7. Using kibitz From Other Expect Scripts
      8. Mailing From Expect
      9. A Manager For Disconnected Processes—dislocate
      10. Expect As A Daemon
      11. Example—Automating Gopher and Mosaic telnet Connections
      12. Exercises
    22. 18. Debugging Scripts
      1. Tracing
      2. Logging
      3. Command Tracing
      4. Variable Tracing
      5. Example—Logging By Tracing
      6. UNIX System Call Tracing
      7. Tk And tkinspect
      8. Traditional Debugging
      9. Debugger Command Overview And Philosophy
      10. Stepping Over Procedure Calls
      11. Stepping Into Procedure Calls
      12. Where Am I
      13. The Current Scope
      14. Moving Up And Down The Stack
      15. Returning From A Procedure
      16. Continuing Execution
      17. Defining Breakpoints
      18. Help
      19. Changing Program Behavior
      20. Changing Debugger Behavior
      21. Exercises
    23. 19. Expect + Tk = Expectk
      1. Tk—A Brief Technical Overview
      2. Expectk
      3. The send Command
      4. An Extended Example—tkpasswd
      5. The expect Command And The Tk Event Loop
      6. The expect_background Command
      7. Multiple Spawn Ids In expect_background
      8. Background Actions
      9. Example—A Dumb Terminal Emulator
      10. Example—A Smarter Terminal Emulator
      11. Using The Terminal Emulator For Testing And Automation
      12. Exercises
    24. 20. Extended Examples
      1. Encrypting A Directory
      2. File Transfer Over telnet
      3. You Have Unread News—tknewsbiff
      4. Exercises
    25. 21. Expect, C, And C++
      1. Overview
      2. Linking
      3. Include Files
      4. Ptys And Processes
      5. Allocating Your Own Pty
      6. Closing The Connection To The Spawned Process
      7. Expect Commands
      8. Regular Expression Patterns
      9. Exact Matching
      10. Matching A Null
      11. What Characters Matched
      12. When The Number Of Patterns Is Not Known In Advance
      13. Expecting From Streams
      14. Running In The Background
      15. Handling Multiple Inputs And More On Timeouts
      16. Output And Debugging Miscellany
      17. Pty Trapping
      18. Exercises
    26. 22. Expect As Just Another Tcl Extension
      1. Adding Expect To Another Tcl-based Program
      2. Differences Between Expect And The Expect Extension In Another Program
      3. Adding Extensions To Expect
      4. Adding Extensions To Expectk
      5. Creating Script-less Expect Programs
      6. Functions And Variables In The Expect Extension
      7. Exercises
    27. 23. Miscellaneous
      1. Random Numbers
      2. Example—Generating Random Passwords
      3. The Expect Library
      4. Expect Versions
      5. Timestamps
      6. The time Command
      7. Exercises
    28. A. Appendix—Commands and Variables
      1. Commands And Flags
      2. Variables
    29. Index
    30. About the Author
    31. SPECIAL OFFER: Upgrade this ebook with O’Reilly

How To Read This Book

This book can be read from front to back. Each chapter flows naturally into the next, and examples in each chapter only use the concepts that have been introduced up to that point. Of course, you can skip chapters or jump around if you like. But I recommend you come back and read everything eventually. This book is chock-full of examples—and they are really worth seeing. To further stimulate you, exercises at the end of each chapter hint at additional thoughts and applications.

Expect draws together a lot of concepts from different programs and even different operating systems. For this reason it is likely that you are familiar with some pieces but not others. The book is laid out so that it is easy to skip things with which you are already familiar. The Preface provides mostly historical notes, setting the scene for Expect and describing how it came into existence. This is not critical to the use of Expect but it makes interesting reading. You may want to read it later.

Chapter 1 is an overview of Expect, giving a taste of what it can do, why it is worth your attention, who uses it, and how it fits into the world. If you know little or nothing about Expect and would like to quickly know what it is all about, read this chapter rather than flipping through the book.

Chapter 2 is an overview of Tcl, the language that Expect uses. Tcl is used by many other software packages so you may already know it—I encourage you to read Chapter 2 anyway. Even if you know Tcl already, you will find that aspects of the language that Expect relies upon are different than in other Tcl tools. Chapter 2 emphasizes these aspects and at the same time puts the rest of Tcl into a consistent framework so that it all fits together.

After Chapter 2 comes the meat of the book—chapters that focus on different parts of Expect starting with automating simple interactions and ending with sophisticated and complex applications that use multiple processes and graphic front-ends. The chapter names are suggestive of the main concepts covered in each chapter; however, all of the chapters include many other concepts that are easier to explain in the context of the chapters they are in. This makes the titles a little less helpful, but the Extended Table Of Contents lists all of the concept headings of each chapter.

Near the end of the book are several chapters on subjects that may not be of interest to everyone. For instance, one such chapter is how to use Expect with Tk; another is how to use Expect from C or C++ (without Tcl). There is also a chapter on embedding Expect in with your own Tcl extensions. That particular chapter assumes that you have read the Tcl reference documentation on the C interface.

The last chapter contains some topics that did not deserve their own chapters nor did they fit in any others. The concepts there are not that important but may be useful nonetheless.

I believe strongly in thorough indexes and there are two in this book so that you can find any item even if it is not in the Extended Table of Contents. The primary index cross-references all concepts, commands, examples, and figures. Many of the examples in the book are interesting in their own right and you will want to use them as tools on their own. In order to find your way back to them, another index lists the substantive examples. Most of these are also available in machine-readable form with the Expect distribution itself. I will describe how to obtain the distribution in Chapter 1 (p. 16)

There is also an appendix that contains a list of all of the Expect commands and variables. Each entry has a brief description and a page number back to the body of the book where you can get the full explanation. I recommend you turn to page 525 and dog-ear it right now!

Most of the chapters are heavily illustrated with code fragments. Code-reading is essential to see how things look in context. And the more code to which you are exposed, the more ideas you can learn. It is also important to see larger pieces of code, and I have provided several significantly bigger programs in chapters towards the rear of the book. Unlike most programs found in the Tcl archives, the ones in this book are extensively and carefully described.

Finally, a gentle warning before you start reading—this book describes how to use Expect, but it is not a reference manual. While terse and lacking in background and examples, the man page that comes with the Expect software is always the latest and most accurate documentation. If Expect changes, it will be reflected there.

Notational Conventions

Body text is set in ITC Garamond Light. Terms being defined or emphasized are italicized. Parameterized input or output (i.e., rmfilename) appears as Courier Italic. Courier is used for source code, files, hostnames, literal I/O, or anything that is computer input or output. Characters typed by a person are in Courier Bold. Due to the nature of Expect, it may sometimes appear that a person has typed something when in reality it was typed by Expect. Thus, the boldness of the font will be helpful in these otherwise misleading situations.

Straight quotes (' or " or ') are used when they are literally part of the characters or strings. Curly quotes (“”) are occasionally used to distinguish literal text from the surrounding text or nearby punctuation if it might not otherwise be obvious (or for consistency with other strings in the same sentence).

Inter-chapter references such as "Chapter 1 (p. 19)” include page numbers describing exactly where in the chapter the referenced topic appears. In this example, the discussion of Expect and Tcl resources appears in the first chapter and the discussion itself begins on page 19.

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