Advanced Bash-Scripting Guide An in-depth exploration of the art of shell scripting Mendel Cooper <[email protected]> 5.1 10 November 2007 Revision History Revision 4.3 29 Apr 2007 Revised by: mc 'INKBERRY' release: Minor Update. Revision 5.0 24 Jun 2007 Revised by: mc 'SERVICEBERRY' release: Major Update. Revision 5.1 10 Nov 2007 Revised by: mc 'LINGONBERRY' 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 snippets 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..................................................................................27 4.1. Variable Substitution......................................................................................................................27 4.2. Variable Assignment.......................................................................................................................30 4.3. Bash Variables Are Untyped..........................................................................................................31 4.4. Special Variable Types...................................................................................................................32 Chapter 5. Quoting...........................................................................................................................................37 5.1. Quoting Variables...........................................................................................................................37 5.2. Escaping..........................................................................................................................................39 Chapter 6. Exit and Exit Status.......................................................................................................................44 Chapter 7. Tests................................................................................................................................................46 7.1. Test Constructs...............................................................................................................................46 7.2. File test operators............................................................................................................................52 7.3. Other Comparison Operators..........................................................................................................55 7.4. Nested if/then Condition Tests.......................................................................................................60 7.5. Testing Your Knowledge of Tests..................................................................................................60 Chapter 8. Operations and Related Topics....................................................................................................62 8.1. Operators.........................................................................................................................................62 8.2. Numerical Constants.......................................................................................................................68 Part 3. Beyond the Basics.................................................................................................................................70 Chapter 9. Variables Revisited........................................................................................................................71 9.1. Internal Variables............................................................................................................................71 9.2. Manipulating Strings.......................................................................................................................88 9.2.1. Manipulating strings using awk............................................................................................95 9.2.2. Further Discussion.................................................................................................................96 9.3. Parameter Substitution....................................................................................................................96 9.4. Typing variables: declare or typeset.............................................................................................105 9.5. Indirect References.......................................................................................................................107 9.6. $RANDOM: generate random integer..........................................................................................110 9.7. The Double Parentheses Construct...............................................................................................121 i Advanced Bash-Scripting Guide Table of Contents Chapter 10. Loops and Branches..................................................................................................................123 10.1. Loops..........................................................................................................................................123 10.2. Nested Loops..............................................................................................................................135 10.3. Loop Control...............................................................................................................................136 10.4. Testing and Branching................................................................................................................139 Chapter 11. Command Substitution.............................................................................................................147 Chapter 12. Arithmetic Expansion................................................................................................................153 Chapter 13. Recess Time................................................................................................................................154 Part 4. Commands..........................................................................................................................................155 Chapter 14. Internal Commands and Builtins.............................................................................................163 14.1. Job Control Commands..............................................................................................................190 Chapter 15. External Filters, Programs and Commands...........................................................................195 15.1. Basic Commands........................................................................................................................195 15.2. Complex Commands...................................................................................................................200 15.3. Time / Date Commands..............................................................................................................210 15.4. Text Processing Commands........................................................................................................213 15.5. File and Archiving Commands...................................................................................................234 15.6. Communications Commands......................................................................................................251 15.7. Terminal Control Commands.....................................................................................................265 15.8. Math Commands.........................................................................................................................266 15.9. Miscellaneous Commands..........................................................................................................275 Chapter 16. System and Administrative Commands..................................................................................289