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Unix Shell Programming, Third Edition

Name: Unix Shell Programming, Third Edition
Author: Stephen G. Kochan
ISBN: 0672324903

by Stephen G. Kochan

February 2003

Intermediate to advanced

456 pages

11h 8m

English

Sams

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About This eBook
Title Page
Copyright Page
Contents at a Glance
Table of Contents
About the Authors
Dedication Page
We Want to Hear from You!
Reader Services
1. Introduction

2. A Quick Review of the Basics
Some Basic CommandsDisplaying the Date and Time: The date CommandFinding Out Who’s Logged In: The who CommandEchoing Characters: The echo CommandWorking with FilesListing Files: The ls CommandDisplaying the Contents of a File: The cat CommandCounting the Number of Words in a File: The wc CommandCommand OptionsMaking a Copy of a File: The cp CommandRenaming a File: The mv CommandRemoving a File: The rm CommandWorking with DirectoriesThe Home Directory and PathnamesDisplaying Your Working Directory: The pwd CommandChanging Directories: The cd CommandMore on the ls CommandCreating a Directory: The mkdir CommandCopying a File from One Directory to AnotherMoving Files Between DirectoriesLinking Files: The ln CommandRemoving a Directory: The rmdir CommandFilename SubstitutionThe AsteriskMatching Single CharactersStandard Input/Output and I/O RedirectionStandard Input and Standard OutputOutput RedirectionInput RedirectionPipesFiltersStandard ErrorMore on CommandsTyping More Than One Command on a LineSending a Command to the BackgroundThe ps CommandCommand SummaryExercises
3. What Is the Shell?
The Kernel and the UtilitiesThe Login ShellTyping Commands to the ShellThe Shell’s ResponsibilitiesProgram ExecutionVariable and Filename SubstitutionI/O RedirectionPipeline HookupEnvironment ControlInterpreted Programming Language
4. Tools of the Trade
Regular ExpressionsMatching Any Character: The Period (.)Matching the Beginning of the Line: The Caret (^)Matching the End of the Line: The Dollar Sign ($)Matching a Choice of Characters: The [...] ConstructMatching Zero or More Characters: The Asterisk (*)Matching a Precise Number of Characters: \{...\} Saving Matched Characters: $...$ cut The -d and -f OptionspasteThe -d OptionThe -s Option sed The -n OptionDeleting Lines tr The -s OptionThe –d Option grep Regular Expressions and grep The -v OptionThe -l OptionThe -n OptionsortThe -u OptionThe -r OptionThe -o OptionThe -n OptionSkipping FieldsThe -t OptionOther Options uniq The -d OptionOther OptionsExercises
5. And Away We Go
Command FilesCommentsVariablesDisplaying the Values of VariablesThe Null ValueFilename Substitution and VariablesThe ${variable} ConstructBuilt-in Integer ArithmeticExercises
6. Can I Quote You on That?
The Single QuoteThe Double QuoteThe BackslashUsing the Backslash for Continuing LinesThe Backslash Inside Double QuotesCommand SubstitutionThe Back QuoteThe $(...) ConstructThe expr CommandExercises
7. Passing Arguments
The $# VariableThe $* VariableA Program to Look Up Someone in the Phone BookA Program to Add Someone to the Phone BookA Program to Remove Someone from the Phone Book${n}The shift CommandExercises
8. Decisions, Decisions
Exit StatusThe $? VariableThe test CommandString OperatorsAn Alternative Format for test Integer OperatorsFile OperatorsThe Logical Negation Operator ! The Logical AND Operator –a ParenthesesThe Logical OR Operator –o The else ConstructThe exit CommandA Second Look at the rem ProgramThe elif ConstructYet Another Version of rem The case CommandSpecial Pattern Matching CharactersThe -x Option for Debugging ProgramsBack to the case The Null Command : The && and || ConstructsExercises
9. ’Round and ’Round She Goes
The for CommandThe $@ VariableThe for Without the ListThe while CommandThe until CommandMore on LoopsBreaking Out of a LoopSkipping the Remaining Commands in a LoopExecuting a Loop in the BackgroundI/O Redirection on a LoopPiping Data Into and Out of a LoopTyping a Loop on One LineThe getopts CommandExercises
10. Reading and Printing Data
The read CommandA Program to Copy FilesSpecial echo Escape CharactersAn Improved Version of mycp A Final Version of mycp A Menu-Driven Phone ProgramThe $$ Variable and Temporary FilesThe Exit Status from read The printf CommandExercises
11. Your Environment
Local VariablesSubshellsExported Variables export -p PS1 and PS2 HOME, JamesYour PATH Your Current Directory CDPATH More on SubshellsThe . CommandThe exec CommandThe (...) and { ...; } ConstructsAnother Way to Pass Variables to a SubshellYour .profile FileThe TERM VariableThe TZ VariableExercises
12. More on Parameters
Parameter Substitution ${parameter} ${parameter:-value} ${parameter:=value} ${parameter:?value} ${parameter:+value}Pattern Matching Constructs ${#variable}The $0 VariableThe set CommandThe -x Option set with No ArgumentsUsing set to Reassign Positional ParametersThe -- OptionOther Options to set The IFS VariableThe readonly CommandThe unset CommandExercises
13. Loose Ends
The eval CommandThe wait CommandThe $! VariableThe trap Command trap with No ArgumentsIgnoring SignalsResetting TrapsMore on I/O <&- and >&- Inline Input RedirectionShell ArchivesFunctionsRemoving a Function DefinitionThe return CommandThe type CommandExercises
14. Rolo Revisited
Design Considerations rolo add lu display rem change listall Sample OutputExercises
15. Interactive and Nonstandard Shell Features
Getting the Right ShellThe ENV FileCommand-Line EditingCommand HistoryThe vi Line Edit ModeAccessing Commands from Your HistoryThe Line Edit ModeAccessing Commands from Your HistoryOther Ways to Access Your HistoryThe history CommandThe fc CommandThe r CommandFunctionsLocal VariablesAutomatically Loaded FunctionsInteger ArithmeticInteger TypesNumbers in Different BasesThe alias CommandRemoving AliasesArraysJob ControlStopped Jobs and the fg and bg CommandsThe Restricted Shell rsh Miscellaneous FeaturesOther Features of the cd CommandTilde SubstitutionOrder of SearchCompatibility SummaryExercises
A. Shell Summary
StartupCommandsCommentsParameters and VariablesShell VariablesPositional ParametersSpecial ParametersParameter SubstitutionCommand Re-entryThe fc Command vi Line Edit ModeQuotingTilde SubstitutionArithmetic ExpressionsFilename SubstitutionI/O RedirectionExported Variables and Subshell ExecutionThe (...) ConstructThe { ...; } ConstructMore on Shell VariablesFunctionsJob ControlShell JobsStopping JobsCommand SummaryThe : CommandThe . CommandThe alias CommandThe bg CommandThe break CommandThe case CommandThe cd CommandThe continue commandThe echo CommandThe eval CommandThe exec CommandThe exit CommandThe export CommandThe false CommandThe fc CommandThe fg CommandThe for CommandThe getopts CommandThe hash CommandThe if CommandThe jobs CommandThe kill CommandThe newgrp CommandThe pwd CommandThe read CommandThe readonly CommandThe return CommandThe set CommandThe shift CommandThe test CommandThe times CommandThe trap CommandThe true CommandThe type CommandThe umask CommandThe unalias CommandThe unset CommandThe until CommandThe wait CommandThe while Command
B. For More Information
Online DocumentationDocumentation on the WebBooksO’Reilly & AssociatesSams and QueOther Publishers
Index
Code Snippets

Content preview from Unix Shell Programming, Third Edition

8. Decisions, Decisions

In This Chapter

• Exit Status

• The test Command

• The else Construct

• The exit Command

• The elif Construct

• The case Command

• The Null Command :

• The && and || Constructs

• Exercises

This chapter introduces a statement that is present in almost all programming languages: if. It enables you to test a condition and then change the flow of program execution based on the result of the test.

The general format of the if command is

if command_tthen command command ...fi

where command_t is executed and its exit status is tested. If the exit status is zero, the commands that follow between the then and the fi are executed; otherwise, they are skipped.

Exit Status

Whenever any program completes execution under ...

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Shell Programming in Unix, Linux and OS X, Fourth Edition

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Unix Shell Programming, Third Edition

by Stephen G. Kochan