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A compendium of shell scripting recipes that can immediately be used, adjusted, and applied The shell is the primary way of communicating with the Unix and Linux systems, providing a direct way to program by automating simple-to-intermediate tasks. With this book, Linux expert Steve Parker shares a collection of shell scripting recipes that can be used as is or easily modified for a variety of environments or situations. The book covers shell programming, with a focus on Linux and the Bash shell; it provides credible, real-world relevance, as well as providing the flexible tools to get started immediately. Shares a collection of helpful shell scripting recipes that can immediately be used for various of real-world challenges Features recipes for system tools, shell features, and systems administration Provides a host of plug and play recipes for to immediately apply and easily modify so the wheel doesn't have to be reinvented with each challenge faced Come out of your shell and dive into this collection of tried and tested shell scripting recipes that you can start using right away! A compendium of shell scripting recipes that can immediately be used, adjusted, and applied The shell is the primary way of communicating with the Unix and Linux systems, providing a direct way to program by automating simple-to-intermediate tasks. With this book, Linux expert Steve Parker shares a collection of shell scripting recipes that can be used as is or easily modified for a variety of environments or situations. The book covers shell programming, with a focus on Linux and the Bash shell; it provides credible, real-world relevance, as well as providing the flexible tools to get started immediately. Shares a collection of helpful shell scripting recipes that can immediately be used for various of real-world challenges Features recipes for system tools, shell features, and systems administration Provides a host of plug and play recipes for to immediately apply and easily modify so the wheel doesn't have to be reinvented with each challenge faced Come out of your shell and dive into this collection of tried and tested shell scripting recipes that you can start using right away! Introduction xxix Part I: About the Ingredients Chapter 1: The History of Unix, Gnu, and Linux 3 Unix 3 "Everything is a File" and Pipelines 5 BSD 6 GNU 7 Linux 11 Summary 12 Chapter 2: Getting Started 15 Choosing an OS 15 GNU/Linux 15 The BSDs 17 Proprietary Unix 17 Microsoft Windows 17 Choosing an Editor 18 Graphical Text Editors 18 Terminal Emulation 21 Nongraphical Text Editors 22 Setting Up the Environment 24 The Shell Profile 24 Aliases 26 vim Settings 30 Summary 31 Chapter 3: Variables 33 Using Variables 33 Typing 34 Assigning Values to Variables 35 Positional Parameters 39 Return Codes 42 Unsetting Variables 45 Preset and Standard Variables 47 BASH_ENV 47 BASHOPTS 47 SHELLOPTS 48 BASH_COMMAND 50 BASH_SOURCE, FUNCNAME, LINENO, and BASH_LINENO 51 SHELL 55 HOSTNAME and HOSTTYPE 55 Working Directory 55 PIPESTATUS 55 TIMEFORMAT 56 PPID 57 RANDOM 58 REPLY 58 SECONDS 58 BASH_XTRACEFD 59 GLOBIGNORE 60 HOME 62 IFS 62 PATH 63 TMOUT 64 TMPDIR 65 User Identification Variables 65 Summary 66 Chapter 4: Wildcard Expansion 67 Filename Expansion (Globbing) 67 Bash Globbing Features 70 Shell Options 71 Regular Expressions and Quoting 75 Overview of Regular Expressions 76 Quoting 77 Summary 81 Chapter 5: Conditional Execution 83 If/Then 83 Else 85 elif 85 Test ([) 87 Flags for Test 88 File Comparison Tests 95 String Comparison Tests 96 Regular Expression Tests 98 Numerical Tests 101 Combining Tests 103 Case 105 Summary 109 Chapter 6: Flow Control Using Loops 111 For Loops 111 When to Use for Loops 112 Imaginative Ways of Feeding "for" with Data 112 C-Style for Loops 118 while Loops 119 When to Use while Loops 119 Ways to Use while Loops 119 Nested Loops 125 Breaking and Continuing Loop Execution 126 while with Case 130 until Loops 131 select Loops 133 Summary 137 Chapter 7: Variables Continued 139 Using Variables 139 Variable Types 141 Length of Variables 142 Special String Operators 144 Stripping Variable Strings by Length 144 Stripping from the End of the String 146 Stripping Strings with Patterns 147 Searching Strings 151 Using Search and Replace 151 Replacing Patterns 153 Deleting Patterns 153 Changing Case 153 Providing Default Values 153 Indirection 157 Sourcing Variables 158 Summary 159 Chapter 8: Functions and Libraries 161 Functions 161 Defining Functions 162 Function Output 162 Writing to a File 164 Redirecting the Output of an Entire Function 167 Functions with Trap 171 Recursive Functions 173 Variable Scope 177 Libraries 181 Creating and Accessing Libraries 183 Library Structures 183 Network Configuration Library 187 Use of Libraries 191 getopts 191 Handling Errors 194 getopts within Functions 195 Summary 197 Chapter 9: Arrays 199 Assigning Arrays 199 One at a Time 200 All at Once 200 By Index 201 All at Once from a Source 201 Read from Input 203 Accessing Arrays 205 Accessing by Index 205 Length of Arrays 206 Accessing by Variable Index 206 Selecting Items from an Array 209 Displaying the Entire Array 209 Associative Arrays 210 Manipulating Arrays 211 Copying an Array 211 Appending to an Array 213 Deleting from an Array 214 Advanced Techniques 216 Summary 217 Chapter 10: Processes 219 The ps Command 219 ps Line Length 220 Parsing the Process Table Accurately 220 killall 223 The /proc pseudo-filesystem 225 prtstat 226 I/O Redirection 227 Appending Output to an Existing File 229 Permissions on Redirections 229 exec 229 Using exec to Replace the Existing Program 230 Using exec to Change Redirection 231 Pipelines 237 Background Processing 237 wait 238 Catching Hangups with nohup 239 Other Features of /proc and /sys 242 Version 242 SysRq 242 /proc/meminfo 245 /proc/cpuinfo 245 /sys 246 /sys/devices/system/node 251 sysctl 253 Summary 254 Chapter 11: Choosing and Using Shells 255 The Bourne Shell 256 The KornShell 256 The C Shell 256 The Tenex C Shell 257 The Z Shell 257 The Bourne Again Shell 257 The Debian Almquist Shell 258 Dotfiles 258 Interactive Login Shells 259 Interactive Non-Login Shells 260 Non-Interactive Shells 261 Logout Scripts 262 Command Prompts 262 The PS1 Prompt 262 The PS2, PS3, and PS4 Prompts 264 Aliases 265 Timesavers 265 Modifying Behaviors 265 History 266 Recalling Commands 267 Searching History 267 Timestamps 268 Tab Completion 269 ksh 269 tcsh 270 zsh 270 bash 271 Foreground, Background, and Job Control 272 Backgrounding Processes 272 Job Control 273 nohup and disown 275 Summary 276 Part II: Recipes For Using and Extending System Tools Chapter 12: File Manipulation 279 stat 279 cat 281 Numbering Lines 282 Dealing with Blank Lines 282 Non-Printing Characters 283 cat Backwards is tac 284 Redirection 285 Redirecting Output: The Single Greater-Than Arrow (>) 285 Appending: The Double Greater-Than Arrow (>>) 286 Input Redirection: The Single Less-Than Arrow (<) 288 Here Documents: The Double Less-Than Arrow (<< EOF) 290 dd 292 df 294 mktemp 295 join

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