Advanced Bash-Scripting Guide An in-depth exploration of the art of shell scripting Mendel Cooper <[email protected]> 5.5 23 November 2008 Revision History Revision 5.3 05 May 2008 Revised by: mc 'GOLDENBERRY' release: Minor Update. Revision 5.4 21 July 2008 Revised by: mc 'ANGLEBERRY' release: Major Update. Revision 5.5 23 Nov 2008 Revised by: mc 'FARKLEBERRY' release: Minor Update. This tutorial assumes no previous knowledge of scripting or programming, but progresses rapidly toward an intermediate/advanced level of instruction . all the while sneaking in little nuggets of UNIX® wisdom and lore. It serves as a textbook, a manual for self-study, and a reference and source of knowledge on shell scripting techniques. The exercises and heavily-commented examples invite active reader participation, under the premise that the only way to really learn scripting is to write scripts. This book is suitable for classroom use as a general introduction to programming concepts. The latest update of this document, as an archived, bzip2-ed "tarball" including both the SGML source and rendered HTML, may be downloaded from the author's home site. A pdf version is also available ( pdf mirror site). See the change log for a revision history. Dedication For Anita, the source of all the magic Advanced Bash-Scripting Guide Table of Contents Chapter 1. Why Shell Programming?...............................................................................................................1 Chapter 2. Starting Off With a Sha-Bang........................................................................................................3 2.1. Invoking the script............................................................................................................................6 2.2. Preliminary Exercises.......................................................................................................................6 Part 2. Basics.......................................................................................................................................................7 Chapter 3. Special Characters...........................................................................................................................8 Chapter 4. Introduction to Variables and Parameters..................................................................................28 4.1. Variable Substitution......................................................................................................................28 4.2. Variable Assignment.......................................................................................................................31 4.3. Bash Variables Are Untyped..........................................................................................................32 4.4. Special Variable Types...................................................................................................................33 Chapter 5. Quoting...........................................................................................................................................39 5.1. Quoting Variables...........................................................................................................................39 5.2. Escaping..........................................................................................................................................41 Chapter 6. Exit and Exit Status.......................................................................................................................47 Chapter 7. Tests................................................................................................................................................49 7.1. Test Constructs...............................................................................................................................49 7.2. File test operators............................................................................................................................56 7.3. Other Comparison Operators..........................................................................................................59 7.4. Nested if/then Condition Tests.......................................................................................................64 7.5. Testing Your Knowledge of Tests..................................................................................................65 Chapter 8. Operations and Related Topics....................................................................................................66 8.1. Operators.........................................................................................................................................66 8.2. Numerical Constants.......................................................................................................................72 Part 3. Beyond the Basics.................................................................................................................................74 Chapter 9. Variables Revisited........................................................................................................................75 9.1. Internal Variables............................................................................................................................75 9.2. Manipulating Strings.......................................................................................................................92 9.2.1. Manipulating strings using awk..........................................................................................100 9.2.2. Further Reference................................................................................................................100 9.3. Parameter Substitution..................................................................................................................101 9.4. Typing variables: declare or typeset.............................................................................................110 9.4.1. Another use for declare.......................................................................................................112 9.5. Indirect References.......................................................................................................................112 9.6. $RANDOM: generate random integer..........................................................................................116 9.7. The Double-Parentheses Construct...............................................................................................127 i Advanced Bash-Scripting Guide Table of Contents Chapter 10. Loops and Branches..................................................................................................................129 10.1. Loops..........................................................................................................................................129 10.2. Nested Loops..............................................................................................................................142 10.3. Loop Control...............................................................................................................................143 10.4. Testing and Branching................................................................................................................146 Chapter 11. Command Substitution.............................................................................................................155 Chapter 12. Arithmetic Expansion................................................................................................................161 Chapter 13. Recess Time................................................................................................................................162 Part 4. Commands..........................................................................................................................................163 Chapter 14. Internal Commands and Builtins.............................................................................................171 14.1. Job Control Commands..............................................................................................................199 Chapter 15. External Filters, Programs and Commands...........................................................................204 15.1. Basic Commands........................................................................................................................204 15.2. Complex Commands...................................................................................................................209 15.3. Time / Date Commands..............................................................................................................219 15.4. Text Processing Commands........................................................................................................223 15.5. File and Archiving Commands...................................................................................................245 15.6. Communications Commands......................................................................................................263 15.7. Terminal Control Commands.....................................................................................................277 15.8. Math Commands.........................................................................................................................278 15.9. Miscellaneous Commands..........................................................................................................289