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SuSE Linux Enterprise Server
Shell Programming with the Bash Shell
SuSE Linux AG
SuSE Linux AG
Training Document – Article No. 45361-2INT
SuSE Linux Enterprise Server
Authors: Peter Albrecht, Anke Börnig, Berthold Gunreben, Marion Reyzl, Jesko Schneider, Dr.
Oliver Schrögel, Dieter Thalmayr, Michael Weyrauch
Release: January 2004 (SuSE Linux Enterprise Server 8)
Translation/Editing: Olaf Niepolt, Steve Tomlin, Tino Tanner
All programs, illustrations and information contained in this manual were compiled to our best
knowledge and tested carefully. This, however, does not exclude the possibility of errors. For this
reason, the program material contained in this present manual shall not constitute any obligation or
guarantee of any kind. The authors of SuSE Linux AG will thus accept no responsibility or in any
way be held liable for damages of any kind which may result from the use of this program material,
parts thereof, or for any resulting violation of the law by third parties.
The representation of registered names, trade names, the naming of goods etc. in this training
manual does not give the right, even where not specifically stipulated, to assume that such names,
in terms of trade names or protection of trade name legislation, can be regarded as free and thus be
put to use by anybody whosoever.
All trade names are used without the guarantee for their free use and may possibly be registered
trade marks. SuSE Linux AG essentially adheres to the guidelines of the manufacturers. Other
products named here may be trade marks of a respective manufacturer.
This work is protected by copyright. All rights in connection with the reproduction or copying
of this training manual or parts thereof are reserved. This also applies to translations thereof. No
part of this work may, in any form whatsoever (print, photocopy, microfilm or any other proce-
dures) and also not for training purposes, be reproduced or electronically processed, duplicated, or
disseminated without the written permission of the publisher.
© 2003 SuSE Linux AG
Contents
1 Introduction
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1.1 Shells .
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1.2 Types of Unix Shells
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1.3 Uses for Shell Scripts .
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1.4 Advantages of Shell Scripts .
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2 Bash Basics
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2.1 Initialization Files
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2.1.1 Login Shells
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2.1.2 Non-Login Shells
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2.2 Aliases
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2.3 Variables
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2.3.1 Working With Variables .
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2.3.2 Important Internal Bash Variables
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2.4 Command History
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2.5 Input and Output Channels .
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2.5.1 Redirection to Files .
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2.5.2 The
here
Operator
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2.5.3 Feeding Output to Another Process .
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2.5.4 Duplicating the Output with
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2.6 Types of Commands
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2.7 Quoting
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2.8 Substitution and Expansion .
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2.8.1 Variable Substitution
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2.8.2 Filename Expansion (File Globbing)
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2.8.3 Command Substitution
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2.8.4 Arithmetic Substitution
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2.9 Command-Line Interpretation
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2.9.1 Command Separators
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3 Basic Script Elements 1 (Input, Output)
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3.1 Program Flow Charts .
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3.2 General Considerations
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3.3 Producing Output From a Script .
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3.4 Reading User Input
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3.5 Simple Operations with Variables
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3.5.1 Basic String Operations .
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3.5.2 Arithmetic Operations
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4 Basic Script Elements 2 (Control Structures)
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4.1 Simple Branching With
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4.1.1 Short Forms of
if
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4.2 Multiple Branches With
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4.3 Iterations and Loops
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4.3.1 Looping With
while
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until
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4.3.2 Processing a List With
for
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4.4 Exiting From a Loop
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4.4.1 Exiting From the Current Loop Iteration with
continue
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4.4.2 Exiting from a Loop with
break
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ii
Contents
5 Advanced Scripting Techniques
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5.1 Reading Input With
read
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5.2 Shell Functions
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5.3 Reading Options With
getopts
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5.4 Signal Handling With
trap
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5.5 Implementing Simple Menus with
select
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5.6 Dialog Boxes With
dialog
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5.6.1 Yes/No Box (
yesno
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5.6.2 Message Box (
msgbox
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5.6.3 Input Box (
inputbox
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5.6.4 Text Box (
textbox
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5.6.5 Menu Box (
menu
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5.6.6 Check List Box (
checklist
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5.6.7 Radio List Box (
radiolist
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5.6.8 Progress Meter Box(
gauge
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A Useful Commands for Shell Scripts
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A.1
cat
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A.2
cut
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A.3
date
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A.4
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A.5
grep
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egrep
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A.6
sed
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A.7
test
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A.8
tr
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B Regular Expressions
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C Special Variable Substitution Operators for Bash
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D Debugging Shell Scripts
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E Sample Scripts
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iii
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