Shell Programming for System Administrators Student Guide

Shell Programming for System Administrators Student Guide D61776GC21 Edition 2.1 April 2010 D66885

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Table of Contents About This Course...Preface-i Course Goal... Preface-i Course Overview... Preface-ii Course Map...Preface-iii Module-by-Module Overview... Preface-iv Course Objectives... Preface-vii Topics Not Covered...Preface-viii How Prepared Are You?... Preface-ix Introductions... Preface-x How to Use Course Materials... Preface-xi Conventions... Preface-xii Icons... Preface-xii Typographical Conventions...Preface-xiii UNIX Shells and Shell Scripts...1-1 Objectives... 1-1 What Is a Shell?... 1-2 What Are Shell Functions?... 1-3 Command-Line Interpreter... 1-3 Programming Language... 1-3 User Environment... 1-4 Solaris OS Shells... 1-5 The Bourne Shell... 1-5 The C Shell... 1-5 The Korn Shell... 1-6 Additional Solaris OS Shells... 1-7 The GNU Bourne-Again Shell... 1-7 The Desktop Korn Shell... 1-7 The Job Control Shell... 1-8 The Restricted Shell Command Interpreter... 1-8 The Enhanced C Shell... 1-9 Z Shell... 1-9 Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Learning Services, Revision B.1 5

Shells Discussed in This Course... 1-10 Subshells Child Processes... 1-11 What Is a Shell Script?... 1-13 Developing a Script... 1-14 Programming Terminology... 1-15 Logic-Flow Design... 1-16 The echoscript1.sh Example Bourne Script... 1-17 The echoscript2.ksh Example Korn Script... 1-18 The /etc/init.d/volmgt Example Boot Script... 1-19 Exercise: Reviewing UNIX Shells and Shell Scripts... 1-20 Preparation... 1-20 Tasks... 1-20 Exercise Summary... 1-22 Task Solutions... 1-23 Writing and Debugging Scripts... 2-1 Objectives... 2-1 Creating Shell Scripts... 2-2 Executing a Shell Script... 2-3 Executing the firstscript.sh Script... 2-4 Starting a Script With the #! Characters... 2-6 Putting Comments in a Script... 2-7 Adding the Debugging Statement... 2-9 Debug Mode Controls... 2-10 Example: Debug Mode Specified on the #! Line... 2-11 Example: Debug Mode With the set -x Option... 2-13 Example: Debug Mode With the set -v Option... 2-14 Syntax Comparison for Bourne and Korn Shell Options...2-15 Example: Debug Mode With the set -o noglob Option... 2-16 Exercise: Writing Shell Scripts... 2-17 Preparation... 2-17 Tasks... 2-17 Exercise Summary... 2-20 Task Solutions... 2-21 The Shell Environment... 3-1 Objectives... 3-1 User Startup Scripts... 3-2 The /etc/profile Script... 3-2 The $HOME/.profile Script... 3-2 The $HOME/.kshrc Script... 3-3 Modifying a Configuration File... 3-4 Shell Variables... 3-5 Creating Variables in the Shell... 3-7 Exporting Variables to Subshells... 3-9 Reserved Variables... 3-11 Special Shell Variables... 3-12 6 Shell Programming for System Administrators Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Services, Revision B.1

Process Identification... 3-12 Exit Status... 3-12 Background Process Identification... 3-13 Quoting Characters... 3-14 A Pair of Single Quotes... 3-14 A Pair of Double Quotes... 3-15 Backslash... 3-15 The eval Command... 3-16 Shell Command Substitution... 3-17 Korn Shell Tilde Expansion... 3-19 Examples... 3-19 Arithmetic Operations on Bourne Shell Variables... 3-20 Arithmetic Operations on Korn Shell Variables... 3-23 Arithmetic Precedence... 3-24 The Korn Shell let Statement... 3-27 Script Math... 3-28 Korn Shell Aliases... 3-29 Removing Aliases... 3-29 Alias Inheritance... 3-29 Automatic (Tracked) Aliases... 3-30 Built-in Aliases... 3-31 Shell Parse Order... 3-32 Special Characters Precedence... 3-33 Exercise: Using the Shell Environment... 3-34 Preparation... 3-34 Tasks... 3-34 Exercise Summary... 3-37 Task Solutions... 3-38 Regular Expressions and the grep Command...4-1 Objectives... 4-1 The grep Command... 4-2 The grep Options... 4-3 Regular Expression Metacharacters... 4-5 Regular Expressions... 4-6 Escaping a Regular Expression... 4-7 Line Anchors... 4-9 Word Anchors... 4-10 Character Classes... 4-11 Character Match... 4-12 Closure (*)... 4-13 The egrep Command... 4-14 Exercise: Using Regular Expressions and the grep Command... 4-15 Preparation... 4-15 Tasks... 4-15 Exercise Summary... 4-17 Task Solutions... 4-18 Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Learning Services, Revision B.1 7

Using the sed Editor... 5-1 Objectives... 5-1 Introduction to the sed Editor... 5-2 Command Format... 5-3 Editing Commands... 5-4 Addressing... 5-5 Using sed to Print Text... 5-6 Using sed to Substitute Text... 5-8 Reading From a File for New Text... 5-10 Using sed to Delete Text... 5-11 Reading sed Commands From a File... 5-12 Using sed to Write Output Files... 5-13 Exercise: Using the sed Editor... 5-14 Preparation... 5-14 Tasks... 5-14 Exercise Summary... 5-16 Task Solutions... 5-17 The nawk Programming Language... 6-1 Objectives... 6-1 Introduction to the nawk Programming Language... 6-2 Format of the nawk Command... 6-3 Executing nawk Scripts... 6-3 Using nawk to Print Selected Fields... 6-4 Formatting With print Statements... 6-5 Using Regular Expressions... 6-7 The BEGIN and END Special Patterns... 6-9 Using nawk Scripts... 6-11 Using Built-in Variables... 6-12 Working With Variables... 6-13 Input Field Separator... 6-13 Output Field Separator... 6-15 Number of Records... 6-16 Exercise: Using nawk and Regular Expressions... 6-17 Preparation... 6-17 Tasks... 6-17 Exercise Solution... 6-18 User-Defined Variables... 6-19 Adding a Field of Numbers... 6-19 Variable Examples... 6-21 Writing Output to Files... 6-23 The printf() Statement... 6-24 Exercise: Using nawk to Create a Report... 6-26 Tasks... 6-26 Exercise: Using nawk Scripts to process Text Files... 6-27 Preparation... 6-27 8 Shell Programming for System Administrators Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Services, Revision B.1

Tasks... 6-27 Exercise Summary... 6-29 Task Solutions... 6-30 Conditionals...7-1 Objectives... 7-1 The if Statement... 7-2 Parts of the if Statement... 7-4 Command... 7-4 Block of Statements... 7-4 End of the if Statement... 7-4 Exit Status... 7-5 Numeric and String Comparison... 7-6 Syntax for if/then/else Statements... 7-10 Syntax for if/then/elif/else Statements... 7-11 Positional Parameters... 7-14 Using if to Check Command-Line Arguments... 7-15 Creating the USAGE Message... 7-16 Using if to Check Leap Years... 7-18 Nested if Statements... 7-19 Testing File Objects... 7-21 Boolean AND, OR, and NOT Operators... 7-23 The case Statement... 7-26 Example of Using the case Statement... 7-27 Replacing Complex if Statements With a case Statement... 7-29 The exit Statement... 7-31 Exercise: Using Conditionals... 7-33 Preparation... 7-33 Tasks... 7-33 Exercise Summary... 7-36 Task Solutions... 7-37 Interactive Scripts...8-1 Objectives... 8-1 Input and Output in a Script... 8-2 The Korn Shell print Statement... 8-3 Examples of Using the print Statement... 8-4 Examples of Using the echo Statement... 8-5 The read Statement... 8-6 Examples of Using the read Statement... 8-7 Capturing a Command Result... 8-8 Printing a Prompt... 8-9 Prompting for Input Korn Shell Shortcut... 8-11 File Input and Output... 8-13 User-Defined File Descriptors... 8-14 File Descriptors in the Bourne Shell... 8-15 Korn Shell File Descriptors... 8-18 Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Learning Services, Revision B.1 9

The here Document... 8-20 Exercise: Using Interactive Scripts... 8-22 Preparation... 8-22 Tasks... 8-23 Exercise Summary... 8-25 Task Solutions... 8-26 Loops... 9-1 Objectives... 9-1 Shell Loops... 9-2 The for Loop Syntax... 9-3 The for Loop Argument List... 9-4 Using an Explicit List to Specify Arguments... 9-4 Using Variable Contents to Specify Arguments... 9-5 Using Command-Line Arguments to Specify Arguments... 9-6 Using Command Substitution to Specify Arguments... 9-6 Using File Names in Command Substitution to Specify Arguments 9-9 Using File-Name Substitution to Specify Arguments... 9-10 Exercise: Using for Loops... 9-12 Preparation... 9-12 Tasks... 9-12 Task Solutions... 9-13 The while Loop... 9-15 The while Loop Syntax... 9-15 Example of Using a while Loop... 9-17 Keyboard Input... 9-19 Redirecting Input for a while Loop... 9-20 The until Loop... 9-21 The break Statement... 9-22 The continue Statement... 9-23 Example of Using the continue Statement... 9-23 The Korn Shell select Loop... 9-26 The PS3 Reserved Variable... 9-26 Example of Using a select Loop... 9-27 Exiting the select Loop... 9-29 Submenus... 9-31 Example of Using Submenus... 9-31 The for and select Statements Revisited... 9-35 The shift Statement... 9-36 Example of Using the shift Statement... 9-37 Exercise: Using Loops and Menus... 9-39 Preparation... 9-39 Tasks... 9-39 Exercise Summary... 9-41 Task Solutions... 9-42 10 Shell Programming for System Administrators Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Services, Revision B.1

The getopts Statement...10-1 Objective... 10-1 Processing Script Options With the getopts Statement... 10-2 Using the getopts Statement... 10-3 Handling Invalid Options... 10-4 Specifying Arguments to Options... 10-7 Example of Using the getopts Statement... 10-8 Forgetting an Argument to an Option... 10-10 Exercise: Using the getopts Statement... 10-13 Preparation... 10-13 Tasks... 10-13 Exercise Summary... 10-14 Task Solutions... 10-15 Advanced Variables, Parameters, and Argument Lists...11-1 Objectives... 11-1 Variable Types... 11-2 Assessing Variable Values... 11-2 The Korn Shell typeset Statement... 11-3 Example of Using String Manipulations... 11-3 Declaring an Integer Variable... 11-6 Creating Bourne Shell Constants... 11-7 Creating Korn Shell Constants... 11-8 Removing Portions of a String... 11-9 Examples of Removing Portions of a String... 11-9 Korn Shell Arrays... 11-11 Examples of Using Arrays... 11-12 Using the shift Statement With Positional Parameters... 11-14 The Values of the $@" and "$*" Positional Parameters... 11-17 Exercise: Using Advanced Variables, Parameters, and Argument Lists... 11-25 Preparation... 11-22 Tasks... 11-22 Exercise Summary... 11-24 Exercise Solutions... 11-25 Functions...12-1 Objectives... 12-1 Functions in the Shell... 12-2 Syntax... 12-2 Function Execution... 12-2 Positional Parameters and Functions... 12-3 Return Values... 12-5 The typeset and unset Statements... 12-6 Function Files... 12-7 Autoloading Korn Shell Functions With the FPATH Variable... 12-8 Exercise: Using Functions... 12-10 Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Learning Services, Revision B.1 11

Preparation... 12-10 Tasks... 12-10 Exercise Summary... 12-12 Task Solutions... 12-13 Traps... 13-1 Objectives... 13-1 Shell Signal Values... 13-2 Catching Signals With the trap Statement... 13-5 Example of Using the trap Statement... 13-6 Catching User Errors With the trap Statement... 13-9 Example of Using the trap Statement With the ERR Signal... 13-11 When to Declare a trap Statement... 13-13 Exercise: Using Traps... 13-15 Preparation... 13-15 Tasks... 13-15 Exercise Summary... 13-16 Task Solutions... 13-17 Advanced nawk Programming...A-1 Programming Concepts... A-2 The if Statement... A-3 Conditional Printing With the nawk Language... A-4 String Comparisons and Relational and Logical Operators... A-5 Logical Operators... A-6 The while Loop in the nawk Language... A-7 The do while Loop... A-7 The for Loop in the nawk Language... A-9 Using Loops With Arrays... A-10 Nonnumeric Array Indices... A-11 The break and continue Statements... A-13 The continue Statement... A-13 The next and exit Statements... A-15 User-Defined Functions... A-16 Command-Line Arguments... A-18 Using Built-in Variables... A-19 Built-in Arithmetic Functions... A-20 Built-in String Functions... A-21 Built-in I/O Processing Functions... A-23 The printf() Statement... A-24 Built-in Operators... A-25 Additional grep Functionality...B-1 Regular Expression Metacharacters...B-2 Character Classes...B-3 Tagged Regular Expressions...B-5 12 Shell Programming for System Administrators Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Services, Revision B.1

Additional sed Functionality... C-1 Editing Commands...C-2 Placing Multiple Edits in a Single sed Command...C-2 Using sed to Append, Insert, or Change Text...C-3 Shell Metacharacters for Pattern Matching for File Names... D-1 Metacharacter Examples... D-3 UNIX Commands and Utilities... E-1 Status Commands...E-2 The date Command...E-2 The ps Command...E-2 The who Command...E-4 The rusers Command...E-4 The finger Command...E-5 The uptime Command...E-6 The rup Command...E-6 The w Command...E-6 File Access Commands...E-8 The find Command...E-8 The sort Command...E-9 Reading Part of a File...E-12 The tr Command...E-12 The cut Command...E-13 The paste Command...E-15 The cmp, diff, and sdiff Commands...E-16 Combining Commands...E-17 Pipes...E-17 Redirection...E-17 Shell Comparison... F-1 Shell Comparison... F-2 Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. Sun Learning Services, Revision B.1 13