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Learning Linux Shell Scripting

You're reading from   Learning Linux Shell Scripting Leverage the power of shell scripts to solve real-world problems

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Product type Paperback
Published in May 2018
Publisher Packt
ISBN-13 9781788993197
Length 332 pages
Edition 2nd Edition
Languages
Tools
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Author (1):
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Ganesh Sanjiv Naik Ganesh Sanjiv Naik
Author Profile Icon Ganesh Sanjiv Naik
Ganesh Sanjiv Naik
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Table of Contents (17) Chapters Close

Preface 1. Getting Started and Working with Shell Scripting FREE CHAPTER 2. Drilling Deep into Process Management, Job Control, and Automation 3. Using Text Processing and Filters in Your Scripts 4. Working with Commands 5. Exploring Expressions and Variables 6. Neat Tricks with Shell Scripting 7. Performing Arithmetic Operations in Shell Scripts 8. Automating Decision-Making in Scripts 9. Automating Repetitive Tasks 10. Working with Functions 11. Using Advanced Functionality in Scripts 12. System Startup and Customizing a Linux System 13. Pattern Matching and Regular Expressions with sed and awk 14. Taking Backup and Embedding Other Languages in Shell Scripts 15. Database Administration Using Shell Scripts 16. Other Books You May Enjoy

Working with the do – while loop

Similar to the for command, while is also the command for loop operations. The command next to while is evaluated. If it is successful or 0, then the commands inside do and done are executed.

The purpose of a loop is to test a certain condition or expression and execute a given command while the condition is true (the while loop) or until the condition becomes true (the until loop):

while condition

do

commands

done

until condition

do

commands

done

The following is the while_01.sh script in which we read a file and display its
content:

#!/bin/bash 
file=/etc/resolv.conf 
while IFS= read -r line    # IFS : inter field separator 
do 
   # echo line is stored in $line 
  echo $line 
done < "$file" 

Let's test the program:

    $ chmod +x while_01.sh
    $ ./while_01.sh
  

The following will be the output after executing...

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