Bash Guide for Beginners

Machtelt Garrels

Garrels BVBA

<tille wants no spam _at_ garrels dot be>

Version 1.11 Last updated 20081227 Edition

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Table of Contents

Introduction

1. Why this guide?

2. Who should read this book?

3. New versions, translations and availability

4. Revision History

5. Contributions

6. Feedback

7. Copyright information

8. What do you need?

9. Conventions used in this document

10. Organization of this document

1. Bash and Bash scripts

1.1. Common shell programs

1.2. Advantages of the Bourne Again SHell

1.3. Executing commands

1.4. Building blocks

1.5. Developing good scripts

1.6. Summary

1.7. Exercises

2. Writing and debugging scripts

2.1. Creating and running a script

2.2. Script basics

2.3. Debugging Bash scripts

2.4. Summary

2.5. Exercises

3. The Bash environment

3.1. Shell initialization files

3.2. Variables

3.3. Quoting characters

3.4. Shell expansion

3.5. Aliases

3.6. More Bash options

3.7. Summary

3.8. Exercises

4. Regular expressions

4.1. Regular expressions

4.2. Examples using grep

4.3. Pattern matching using Bash features

4.4. Summary

4.5. Exercises

5. The GNU sed stream editor

5.1. Introduction

5.2. Interactive editing

5.3. Non-interactive editing

5.4. Summary

5.5. Exercises

6. The GNU awk programming language

6.1. Getting started with gawk

6.2. The print program

6.3. Gawk variables

6.4. Summary

6.5. Exercises

7. Conditional statements

7.1. Introduction to if

7.2. More advanced if usage

7.3. Using case statements

7.4. Summary

7.5. Exercises

8. Writing interactive scripts

8.1. Displaying user messages

8.2. Catching user input

8.3. Summary

8.4. Exercises

9. Repetitive tasks

9.1. The for loop

9.2. The while loop

9.3. The until loop

9.4. I/O redirection and loops

9.5. Break and continue

9.6. Making menus with the select built-in

9.7. The shift built-in

9.8. Summary

9.9. Exercises

10. More on variables

10.1. Types of variables

10.2. Array variables

10.3. Operations on variables

10.4. Summary

10.5. Exercises

11. Functions

11.1. Introduction

11.2. Examples of functions in scripts

11.3. Summary

11.4. Exercises

12. Catching signals

12.1. Signals

12.2. Traps

12.3. Summary

12.4. Exercises

A. Shell Features

A.1. Common features

A.2. Differing features

Glossary

Index

List of Tables

1. Typographic and usage conventions

1-1. Overview of programming terms

2-1. Overview of set debugging options

3-1. Reserved Bourne shell variables

3-2. Reserved Bash variables

3-3. Special bash variables

3-4. Arithmetic operators

4-1. Regular expression operators

5-1. Sed editing commands

5-2. Sed options

6-1. Formatting characters for gawk

7-1. Primary expressions

7-2. Combining expressions

8-1. Escape sequences used by the echo command

8-2. Options to the read built-in

10-1. Options to the declare built-in

12-1. Control signals in Bash

12-2. Common kill signals

A-1. Common Shell Features

A-2. Differing Shell Features

List of Figures

1. Bash Guide for Beginners front cover

2-1. script1.sh

3-1. Different prompts for different users

6-1. Fields in awk

7-1. Testing of a command line argument with if

7-2. Example using Boolean operators

Consultando una base de datos desde bashy asignando el resultado a una variable

#!/bin/bash
A=$(mysql --user=root --password='19s555' asterisk -e 'SELECT * FROM cdr'; )
echo $A

Haciendo una llamada telefonica desde bash

#!/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
echo " prueba de llamadas $(date)"
$1
$2

B=`asterisk -x "originate SIP/$1 extension $2@internal" `

Script de selection en Bash read

#!/bin/bash
function press_enter
{
echo ""
echo -n "Press Enter to continue"
read
clear
}

selection=
until [ "$selection" = "0" ]; do
echo ""
echo "PROGRAM MENU"
echo "1 - display free disk space"
echo "2 - display free memory"
echo ""
echo "0 - exit program"
echo ""
echo -n "Enter selection: "
read selection
echo ""
case $selection in
1 ) df ; press_enter ;;
2 ) free ; press_enter ;;
0 ) exit ;;
* ) echo "Please enter 1, 2, or 0"; press_enter
esac
done

Bash IF

#!/bin/bash
T1="foo"
T2="bar"
if [ "$T1" = "$T2" ]; then
echo expression evaluated as true
else
echo expression evaluated as false
fi

exportando la ruta de nuestro script

Exportando la ruta de nuestro script
export PATH="$PATH:~/scripts"

http://www.cyberciti.biz/faq/unix-linux-adding-path/

Exportando variables Bash

root@asterisk-dominicana:~# export var1=4566
root@asterisk-dominicana:~# echo $var1
4566
root@asterisk-dominicana:~#

BASH Programming - Introduction HOW-TO

by Mike G mikkey at dynamo.com.ar

Thu Jul 27 09:36:18 ART 2000

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This article intends to help you to start programming basic-intermediate shell scripts. It does not intend to be an advanced document (see the title). I am NOT an expert nor guru shell programmer. I decided to write this because I'll learn a lot and it might be useful to other people. Any feedback will be apreciated, specially in the patch form :)

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1. Introduction

• 1.1 Getting the latest version
• 1.2 Requisites
• 1.3 Uses of this document

2. Very simple Scripts

• 2.1 Traditional hello world script
• 2.2 A very simple backup script

3. All about redirection

• 3.1 Theory and quick reference
• 3.2 Sample: stdout 2 file
• 3.3 Sample: stderr 2 file
• 3.4 Sample: stdout 2 stderr
• 3.5 Sample: stderr 2 stdout
• 3.6 Sample: stderr and stdout 2 file

4. Pipes

• 4.1 What they are and why you'll want to use them
• 4.2 Sample: simple pipe with sed
• 4.3 Sample: an alternative to ls -l *.txt

5. Variables

• 5.1 Sample: Hello World! using variables
• 5.2 Sample: A very simple backup script (little bit better)
• 5.3 Local variables

6. Conditionals

• 6.1 Dry Theory
• 6.2 Sample: Basic conditional example if .. then
• 6.3 Sample: Basic conditional example if .. then ... else
• 6.4 Sample: Conditionals with variables

7. Loops for, while and until

• 7.1 For sample
• 7.2 C-like for
• 7.3 While sample
• 7.4 Until sample

8. Functions

• 8.1 Functions sample
• 8.2 Functions with parameters sample

9. User interfaces

• 9.1 Using select to make simple menus
• 9.2 Using the command line

10. Misc

• 10.1 Reading user input with read
• 10.2 Arithmetic evaluation
• 10.3 Finding bash
• 10.4 Getting the return value of a program
• 10.5 Capturing a commands output
• 10.6 Multiple source files

11. Tables

• 11.1 String comparison operators
• 11.2 String comparison examples
• 11.3 Arithmetic operators
• 11.4 Arithmetic relational operators
• 11.5 Useful commands

12. More Scripts

• 12.1 Applying a command to all files in a directory.
• 12.2 Sample: A very simple backup script (little bit better)
• 12.3 File re-namer
• 12.4 File renamer (simple)

13. When something goes wrong (debugging)

• 13.1 Ways Calling BASH

14. About the document

• 14.1 (no) warranty
• 14.2 Translations
• 14.3 Thanks to
• 14.4 History
• 14.5 More resources

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