Hands-On KornShell93 Programming, 1st edition

  • Barry J. Rosenberg

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Overview

Over the years, KornShell has evolved into a full-featured, powerful shell language. Familiarity with KornShell enables system and network professionals to extend the user environment and automate complex system-administration tasks for huge productivity gains. Bourne and C shell programmers will appreciate KornShell’s superior string handling, stronger data typing, and broader capabilities.

Hands-On KornShell93 Programming is a self-paced tutorial that introduces you to the essentials of KornShell programming. Based almost entirely on short, focused examples that demonstrate central concepts and effective programming techniques, it will quickly bring you up to speed.

The book reflects the newest version of KornShell, KSH93. It also provides coverage of significant developments, such as CGI programming with KornShell, and offers an in-depth look at KornShell string handling.

Humorously written, the book makes it easy to learn KornShell essentials, including data types, math, pattern matching, conditions, loops, menus, command-line arguments, functions, start-up scripts, I/O, strings, variables, background processes, and CGI scripts. Highlighted "Beware" sections will warn you of potential pitfalls and keep you on the track to learning effective KornShell programming.



020131018XB04062001

Table of contents



List of Tables.


List of Figures.


Preface … That No One Will Ever Read.


Author's Note Regarding the ksh93 Edition.


1. Before Writing Your First KornShell Scripts.


2. Getting Started.

What Shell Is Executing My Script?

Operating System Commands in a Shell Script.

BEWARE: Are You Allowed to Execute This Script?

Commenting Your Code.

BEWARE: Picking a Bad Name for Your Script.

The Usage Line.

Simple Output.

Variables.

BEWARE: Variable Names Are Case Sensitive.

Simple Input.

Obtaining the Value of a Variable.

BEWARE: The Dollar Sign in Read Statements.

Newlines, Semicolons, White Space, and Columns.

BEWARE: Confusing + and -.

Assigning a Value to a Variable.

BEWARE: Common Mistakes When Assigning Variables.

Finding Your Mistakes.

Can I Quote You on That?



3. Data Types.

If You're New to Programming … .

If You're an Experienced Programmer … .

Declaring Strings.

Declaring Integers.

Binary, Octal, Hex, and So On.

Declaring Floats.

Declaring Constants.

Declaring nameref Variables.

Declaring Arrays.

Declaring Arrays with set -A.

Printing Array Values.

BEWARE: Common Array Mistakes.

Declaring Associative Arrays.

Probing Arrays.

Declaring Structures Part I.

Declaring Structures Part II.

Arrays of Structures.



4. Math.

If You're New to Programming … .

If You're an Experienced Programmer … .

Double Parentheses.

Integer Addition, Subtraction, and Multiplication.

Integer Division.

Floating-Point Math.

Mixing Floating-Point and Integer Math.

Grouping Mathematical Operations.

BEWARE: Common Mistakes in Math Operations.

Mathematical Assignment Operators.

The Triggy Stuff.

BEWARE: Math Functions Inside Double Parentheses.

A Practical Math Example.

Math Operator Summary.



5. Pattern Matching. If You're New to Programming … .

If You're an Experienced Programmer … .

For Everyone.

The ? Wildcard.

The [char1char2...charN] Wildcard.

Character Classes.

The * Wildcard.

BEWARE: Matching Filenames.

The ?(pattern1|pattern2... |patternN) Wildcard.

BEWARE: White Space within Patterns.

The @(pattern1|pattern2... |patternN) Wildcard.

The *(pattern1|pattern2... |patternN) Wildcard.

The +(pattern1|pattern2... |patternN) Wildcard.

The !(subpattern1|subpattern2... |subpatternN) Wildcard.

Matching Subpatterns with \d.

Simple Commands Containing Patterns.

Wildcard Summary.



6. Conditions.

If You're New to Programming … .

If You're an Experienced Programmer … .

Tests on Numbers and Strings.

Comparing Numbers with if.

BEWARE: Common Mistakes Using if with Numbers.

Comparing Numbers with the ? : Operator.

BEWARE: Common Mistakes in ? :.

Compound Statements.

else and elif.

Comparing Strings with if.

Comparing Alphabetical Order with < and >.

Comparing a String to a Pattern with if.

BEWARE: Common Mistakes Comparing Strings.

Boolean AND, Boolean OR.

The case Statement.

Unexpected Values in a Case Statement.

Wildcards in a Case Statement.

Multiple Patterns in a Case Statement.

BEWARE: Common Mistakes in Case.

Tests on Files, Directories, and the Like.

BEWARE: No Filename Expansion Inside [[ ]].

What Kind of Object Is This?

Boolean NOT.

How Is This Object Protected?

Comparing the Time of Last Modification.

Mixing Tests.



7. Loops.

If You're New to Programming … .

If You're an Experienced Programmer … .

Simple While, Until, and for Loops.

Using While to Average Five Floats.

BEWARE: While Loop Not Guaranteed to Iterate.

Using a C-Style for Loop to Average Five Floats.

Using Break to Leave a Loop.

Using Continue to Skip Part of One Loop Iteration.

Using : to Create an Always True Loop.

BEWARE: The Nature of Truth. Lists in for Loops.

A List of Filenames in a for Loop.

Patterns in a for Loop.

Searching for Objects in Subdirectories.

BEWARE: Nonexistent Patterns.

A Loop within a Loop.

The break Statement within a Nested Loop.



8. Creating Menus.

A Simple Select Example.

A select with a Case.

Unexpected User Input.

Gracefully Exiting from Menus.

Repeating the Menu Selections.

Wildcards in Menu Entries.

Wildcards in case Statements.

A Practical select Example.

Menus Inside of Menus (Submenus).



9. Command Line Arguments and Positional Parameters.

If You're New to Programming … .

If You're an Experienced Programmer … .

Command Line Arguments.

Counting the Number of Command Line Arguments.

Giving the User a Choice of How to Enter Arguments.

BEWARE: Can't Put Positional Parameters to Left of =.

Default Values of Positional Parameters.

Processing Positional Parameters with shift.

Processing Positional Parameters with $* and $@.

“$*” versus “$@” Part 1.

“$*” versus “$@” Part 2.

Using the set Statement to Assign Positional Parameters.

Processing Simple Switches with getopts.

What If the User Enters an Invalid Switch?

On and Off Switches.

Processing Switch Arguments.

Processing Missing Switch Arguments.

A Command Line Containing More Than Just Switches.

BEWARE: The Colon of getopts.

Positional Parameters Syntax Overview.



10. Functions.

If You're New to Programming … .

If You're an Experienced Programmer … .

BEWARE: Two Kinds of Functions.

A Disorganized Script Without Functions.

The Same Script Organized into Functions.

Simple Function with One Argument.

BEWARE: When $1 Isn't the First Command Line Argument.

A Function with Multiple Arguments.

A Script That Calls Another Script.

Two Ways to Return Values.

Returning a Value from a Function with return.

BEWARE: $? Doesn't Stick Around Long.

Using $(...) to Return Values from a Function.

Local Variables versus Global Variables.

BEWARE: Global and Local Variables with the Same Name.

Passing Arrays as Function Arguments: Call-by-Reference.

Sorting Arrays Using Call-by-Value.

Discipline Functions Overview.

Using a .set Discipline Function to Monitor a Variable.

BEWARE: Data Type Declarations and Discipline Functions.

Using a .set Discipline Function to Constrain a Value.

Recursive Functions.

Autoloaded Functions.

BEWARE: Tricky Loading Rules.

Extending the KornShell by Writing C Functions.

Practical Example: The Game of moo.



11. Start-Up Scripts and Environments.

Start-Up Scripts.

Environments.

Dot Scripts.

Aliases.

Example of a $HOME/.profile Start-Up Script.

Example of an Environment (ENV) Script.



12. Input and Output.

If You're New to Programming … .

If You're an Experienced Programmer … .

read, REPLY, and Prompts.

Reading Three Values.

Ignoring Extraneous Input.

Reading Values Having Different Data Types.

Rushing Users to Supply Input.

The IFS Variable.

Input Longer Than One Line.

BEWARE: Put Nothing After the Backslash.

Using a Loop to Process Input.

Reading Text out of a File with <.

Putting < within a Statement.

BEWARE: Common Input Mistakes.

Up Close and Personal with the print Statement.

BEWARE: Bad Options in print Statement.

BEWARE: Wildcards within Strings.

Getting Fancy Output with the printf Statement.

BEWARE: print and printf Handle Newlines Differently.

Redirecting Standard Output with >.

BEWARE: “But It Was Right There a Second Ago!”

Appending with >>.

Mixing < and >.

Pipes.

Streams.

Redirecting Standard Error.

BEWARE: Redirecting Standard Output and Standard Error to Same File.

Opening Files with exec.

Using exec to Do I/O on Multiple Files.

Closing Streams.

Using $(...) to Assign the Output of a Command to a Variable.

Here Documents.



13. Manipulating Strings.

If You're New to Programming … .

If You're an Experienced Programmer … .

Uppercase and Lowercase.

Left Justification.

Concatenating Strings.

Reading an Entire File into One String Variable.

Search and Replace Overview.

Search and Replace Practical Example.

Isolating a Portion of a String.

Removing the Leftmost Characters in a String with #.

Removing the Rightmost Characters in a String with %.

An Application of %.

# versus ##.

% versus %%.

Using # on Numbers.

Deleting a Substring from the Middle of a String.

Pruning Branches from Pathnames.

Matching Multiple Strings on the Same Line.

Finding the Length of a String.

Parsing Strings into Words.

Parsing Strings into Characters.

Specifying Default Values.

Parsing PATH.

Practical Application: Extracting Comments From C Source Code.

String Manipulation Summary.



14. KornShell Reserved Variables.

If You're New to Programming … .

If You're an Experienced Programmer … .

.sh.edchar, .sh.edcol, .sh.edmode, .sh.edtext.

.sh.name, .sh.subscript, and .sh.value.

.sh.version.

ENV.

FIGNORE.

$?-Error Status.

HISTFILE, HISTSIZE, HISTEDIT, HISTCMD, and FCEDIT -History File.

IFS-Parsing Lines into Tokens.

LANG, LC_ALL, LC_COLLATE, LC_TYPE, and LC_NUMERIC.

LINENO-Current Line Number.

MAIL, MAILPATH, and MAILCHECK-Electronic Mail.

OPTARG and OPTIND-Values Associated with getopts.

PATH, CDPATH, and FPATH-Search Directories.

PS1, PS2, PS3, and PS4-Prompts.

BEWARE: Common Mistakes in Setting Prompts.

HOME, PWD, and OLDPWD-Login, Current, and Previous Directories.

RANDOM-Random Integer Generator.

REPLY, -, and _-Miscellaneous Input Repository.

SECONDS-Elapsed Time.

SHELL.

TERM, COLUMN, LINES-Terminal Characteristics.

TMOUT-Time Out an Unused KornShell.

VISUAL and EDITOR-Command Line Text Editors.

$$, $!, and PPID-Process ID.



15. Foreground, Background, and Signaling.

Background and Foreground.

Signaling.

How to Send a Signal to a Script.

Writing Scripts That Respond to Signals.

Catching Signals.

A Trap That Calls Another Script.

Trapping Whenever a Script Exits.

Trapping Whenever Error Status Becomes Nonzero.

Writing Your Own Debugger.

Trapping KEYBD Signals.



16. Command Line Editing and the History File.

What Is Command Line Editing?

What Is a History File?

Listing Previous Commands.

Re-Executing Previous Commands.

BEWARE: Can't Use r on Multiple Commands.

Editing Previous Commands, Then Executing Them.

The Thing You're Going to Do Anyway.

Pathname Completion.

Command Completion.



17. Writing CGI Scripts.

If You're New to CGI Programming … .

If You're an Experienced CGI Programmer … .

Forms.

Text Boxes and Password Boxes.

Checkboxes.

Radio Buttons.

Getting Started Writing CGI Programs.

BEWARE: If Your CGI Script Doesn't Work.

A CGI Script Containing More Than Just print Statements.

File I/O from CGI Scripts.

BEWARE: File Permissions.

Analyzing Form Input: The Get and Post Methods.

The Get Method.

Get Method: Multiple Input Values.

The Post Method.

Handling Special Characters.

Environment Variables Passed by the Web Server.

Browserless Browsing.

BEWARE: Moral Concerns.

Browserless Browsing for GIFs.

BEWARE: When Browserless Browsing Fails.



Appendix A: Statement and Alias Quick Reference.


Appendix B: Just Enough HTML.

Essential HTML Tags.

Headings.

Lists.

Character Tags.

Hyperlinks.

Images.



Bibliography.


Index. 020131018XT04062001

Published by Addison-Wesley Professional (October 13th 1998) - Copyright © 1999