Shell Programming in Unix, Linux and OS X

Stephen Kochan is the author or co-author of several best-selling titles on Unix and the C language, including Programming in C, Programming in Objective-C, Topics in C Programming, and Exploring the Unix System. He is a former software consultant for AT&T Bell Laboratories, where he developed and taught classes on Unix and C programming. Patrick Wood is the CTO of the New Jersey location of Electronics for Imaging. He was a member of the technical staff at Bell Laboratories when he met Mr. Kochan in 1985. Together they founded Pipeline Associates, Inc., a Unix consulting firm, where he was vice president. They co-authored Exploring the Unix System, Unix System Security, Topics in C Programming, and Unix Shell Programming.

1 A Quick Review of the Basics

Some Basic Commands

Displaying the Date and Time: The date Command

Finding Out Who’s Logged In: The who Command

Echoing Characters: The echo Command

Working with Files

Listing Files: The ls Command

Displaying the Contents of a File: The cat Command

Counting the Number of Words in a File: The wc Command

Command Options

Making a Copy of a File: The cp Command

Renaming a File: The mv Command

Removing a File: The rm Command

Working with Directories

The Home Directory and Pathnames

Displaying Your Working Directory: The pwd Command

Changing Directories: The cd Command

More on the ls Command

Creating a Directory: The mkdir Command

Copying a File from One Directory to Another

Moving Files Between Directories

Linking Files: The ln Command

Removing a Directory: The rmdir Command

Filename Substitution

The Asterisk

Matching Single Characters

Filename Nuances

Spaces in Filenames

Other Weird Characters

Standard Input/Output, and I/O Redirection

Standard Input and Standard Output

Output Redirection

Input Redirection

Pipes

Filters

Standard Error

More on Commands

Typing More Than One Command on a Line

Sending a Command to the Background

The ps Command

Command Summary

2 What Is the Shell?

The Kernel and the Utilities

The Login Shell

Typing Commands to the Shell

The Shell’s Responsibilities

Program Execution

Variable and Filename Substitution

I/O Redirection

Hooking up a Pipeline

Environment Control

Interpreted Programming Language

3 Tools of the Trade

Regular Expressions

Matching Any Character: The Period (.)

Matching the Beginning of the Line: The Caret (^)

Matching the End of the Line: The Dollar Sign $

Matching a Character Set: The [...] Construct

Matching Zero or More Characters: The Asterisk (*)

Matching a Precise Number of Subpatterns: /{.../}

Saving Matched Characters: /(.../)

cut

The -d and -f Options

paste

The -d Option

The -s Option

sed

The -n Option

Deleting Lines

tr

The -s Option

The -d Option

grep

Regular Expressions and grep

The -v Option

The -l Option

The -n Option

sort

The -u Option

The -r Option

The -o Option

The -n Option

Skipping Fields

The -t Option

Other Options

uniq

The -d Option

Other Options

4 And Away We Go

Command Files

Comments

Variables

Displaying the Values of Variables

Undefined Variables Have the Null Value

Filename Substitution and Variables

The ${variable} Construct

Built-in Integer Arithmetic

5 Can I Quote You on That?

The Single Quote

The Double Quote

The Backslash

Using the Backslash for Continuing Lines

The Backslash Inside Double Quotes

Command Substitution

The Back Quote

The $(...) Construct

The expr Command

6 Passing Arguments

The $# Variable

The $* Variable

A Program to Look Up Someone in the Phone Book

A Program to Add Someone to the Phone Book

A Program to Remove Someone from the Phone Book

${n}

The shift Command

7 Decisions, Decisions

Exit Status

The $? Variable

The test Command

String Operators

An Alternative Format for test

Integer Operators

File Operators

The Logical Negation Operator !

The Logical AND Operator -a

Parentheses

The Logical OR Operator -o

The else Construct

The exit Command

A Second Look at the rem Program

The elif Construct

Yet Another Version of rem

The case Command

Special Pattern-Matching Characters

The -x Option for Debugging Programs

Back to the case

The Null Command :

The && and || Constructs

8 'Round and 'Round She Goes

The for Command

The $@ Variable

The for Without the List

The while Command

The until Command

More on Loops

Breaking Out of a Loop

Skipping the Remaining Commands in a Loop

Executing a Loop in the Background

I/O Redirection on a Loop

Piping Data into and out of a Loop

Typing a Loop on One Line

The getopts Command

9 Reading and Printing Data

The read Command

A Program to Copy Files

Special echo Escape Characters

An Improved Version of mycp

A Final Version of mycp

A Menu-Driven Phone Program

The $$ Variable and Temporary Files

The Exit Status from read

The printf Command

10 Your Environment

Local Variables

Subshells

Exported Variables

export -p

PS1 and PS2

HOME

PATH

Your Current Directory

CDPATH

More on Subshells

The .Command

The exec Command

The (...) and { ...; } Constructs

Another Way to Pass Variables to a Subshell

Your .profile File

The TERM Variable

The TZ Variable

11 More on Parameters

Parameter Substitution

${parameter}

${parameter:-value}

${parameter:=value}

${parameter:?value}

${parameter:+value}

Pattern Matching Constructs

${#variable}

The $0 Variable

The set Command

The -x Option

set with No Arguments

Using set to Reassign Positional Parameters

The -- Option

Other Options to set

The IFS Variable

The readonly Command

The unset Command

12 Loose Ends

The eval Command

The wait Command

The $! Variable

The trap Command

trap with No Arguments

Ignoring Signals

Resetting Traps

More on I/O

<&- and >&-

In-line Input Redirection

Shell Archives

Functions

Removing a Function Definition

The return Command

The type Command

13 Rolo Revisited

Data Formatting Considerations

rolo

add

lu

display

rem

change

listall

Sample Output

14 Interactive and Nonstandard Shell Features

Getting the Right Shell

The ENV File

Command-Line Editing

Command History

The vi Line Edit Mode

Accessing Commands from Your History

The emacs Line Edit Mode

Accessing Commands from Your History

Other Ways to Access Your History

The history Command

The fc Command

The r Command

Functions

Local Variables

Automatically Loaded Functions

Integer Arithmetic

Integer Types

Numbers in Different Bases

The alias Command

Removing Aliases

Arrays

Job Control

Stopped Jobs and the fg and bg Commands

Miscellaneous Features

Other Features of the cd Command

Tilde Substitution

Order of Search

Compatibility Summary

Appendixes

A Shell Summary

B For More Information