Advanced Bash-Scripting Guide Advanced Bash-Scripting Guide Table of Contents Advanced Bash-Scripting Guide.......................................................................................................................1 An in-depth exploration of the art of shell scripting................................................................................1 Mendel Cooper..................................................................................................................................1 Dedication............................................................................................................................................................3 Part 1. Introduction..........................................................................................................................................15 Chapter 1. Shell Programming!.......................................................................................................................17 Notes......................................................................................................................................................18 Chapter 2. Starting Off With a Sha-Bang......................................................................................................21 2.1. Invoking the script.....................................................................................................................................25 Notes......................................................................................................................................................25 2.2. Preliminary Exercises................................................................................................................................27 Part 2. Basics.....................................................................................................................................................29 Chapter 3. Special Characters.........................................................................................................................31 Notes......................................................................................................................................................50 Chapter 4. Introduction to Variables and Parameters..................................................................................51 4.1. Variable Substitution.................................................................................................................................53 Notes......................................................................................................................................................55 4.2. Variable Assignment..................................................................................................................................57 4.3. Bash Variables Are Untyped.....................................................................................................................59 4.4. Special Variable Types..............................................................................................................................61 Notes......................................................................................................................................................65 Chapter 5. Quoting...........................................................................................................................................67 5.1. Quoting Variables......................................................................................................................................69 Notes......................................................................................................................................................70 5.2. Escaping......................................................................................................................................................73 Chapter 6. Exit and Exit Status.......................................................................................................................79 Notes......................................................................................................................................................81 Chapter 7. Tests................................................................................................................................................83 i Advanced Bash-Scripting Guide Table of Contents 7.1. Test Constructs...........................................................................................................................................85 Notes......................................................................................................................................................92 7.2. File test operators.......................................................................................................................................93 Notes......................................................................................................................................................95 7.3. Other Comparison Operators...................................................................................................................97 Notes....................................................................................................................................................102 7.4. Nested if/then Condition Tests................................................................................................................103 7.5. Testing Your Knowledge of Tests...........................................................................................................105 Chapter 8. Operations and Related Topics..................................................................................................107 8.1. Operators..................................................................................................................................................109 Notes....................................................................................................................................................115 8.2. Numerical Constants...............................................................................................................................117 8.3. The Double-Parentheses Construct........................................................................................................119 8.4. Operator Precedence...............................................................................................................................121 Notes....................................................................................................................................................123 Part 3. Beyond the Basics...............................................................................................................................125 Chapter 9. Another Look at Variables.........................................................................................................127 9.1. Internal Variables....................................................................................................................................129 Notes....................................................................................................................................................147 9.2. Typing variables: declare or typeset......................................................................................................149 9.2.1. Another use for declare..............................................................................................................151 Notes..............................................................................................................................................151 9.3. $RANDOM: generate random integer...................................................................................................153 Notes....................................................................................................................................................163 Chapter 10. Manipulating Variables.............................................................................................................165 10.1. Manipulating Strings.............................................................................................................................167 10.1.1. Manipulating strings using awk...............................................................................................174 10.1.2. Further Reference.....................................................................................................................175 Notes..............................................................................................................................................175 ii Advanced Bash-Scripting Guide Table of Contents 10.2. Parameter Substitution.........................................................................................................................177 Notes....................................................................................................................................................186 Chapter 11. Loops and Branches..................................................................................................................187 11.1. Loops.......................................................................................................................................................189 Notes....................................................................................................................................................202