BASH/C2/More-on-Loops/English
Title of script: Nested loop in Bash
Author: Ashwini Patil
Keywords: video tutorial, for loop
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| Display Slide 1 | Dear friends, Welcome to the spoken tutorial on
Nested for loop in BASH |
| Display Slide 2 | In this tutorial, we will learn
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| Display Slide 3 | For this tutorial I am using
Please note, GNU Bash version 4 or above is recommended to practise this tutorial. |
| Display slide 4
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To learn this tutorial,
you should be familiar with arrays and loops in Bash.
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| Display Slide 5
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Let us start with an introduction.
A loop within a loop is known as nested loop. |
| Display Slide 6 | Let us start with for loop first.
Syntax: for ((exp1; exp2; exp3))
do
for ((exp1; exp2; exp3))
do
statement1
statement1
done
done
Outer for loop expression 1, 2, 3 Inner for loop expression 1, 2, 3 statement 1 statement 2 Closing inner for loop Closing outer for loop
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| Open the file for-new.sh | Let us see an example on for loop |
| Show the folder structure
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First let us go through the directory structure.
Here is a directory on the Desktop named simple-nested-for. Let's open it. |
| Open test directory to show the text files. | We have subdirectories test, test2 and test3 and a bash script.
In each sub-directory there are multiple text files. |
| Now we will move on to our code.
This program displays all the files within each subdirectory.
ls -1 -R test* But we will do it using a for-loop.
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| Point to the filename. | Note that the name of our bash script is nested-for.sh |
| Highlight
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This is our shebang line. |
| Highlight
for dir in test*; do echo "Files in $dir directory:" echo " "
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This is the outer for loop.
This for loop will check for directories starting with the name test . First 'echo' line will display the sub-directories name. The second 'echo' line will create a blank line. |
| for file in $(ls -1 $dir); do
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This is the inner for loop.
It will check for files present within the directories. ls displays the directory content. -1 is used to list one file per line. |
| echo $file
done echo "------------------------" done |
Here we list the files.
'done' ends the inner for loop. This command prints a vertical line after completion of every cycle of outer for-loop. 'done' ends the outer for loop. |
| Open terminal
Ctrl+alt+t Type: cd Desktop/simple-nested-for
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Let us execute the program.
Open the terminal by pressing ctrl+alt+t keys simultaneously on your keyboard. Now let us go to the directory where our bash script is. That is on the desktop. Type cd desktop Let us go in the folder simple-nested-for Press Enter |
| Type:
chmod +x nested-for.sh ./nested-forsh |
Type:
chmod +x nested-for.sh Type: ./nested-for.sh |
| Highlight
Output |
The output is displayed.
It shows
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| This brings us to the end of this tutorial.
Let us summarize. | |
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Summary |
Summary
In this tutorial we learnt, Nested for loop
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Assignment |
As an assignment
Retype the above program using nested while loop. Save your program with the name 'nested-while.sh' |
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http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial About the Spoken Tutorial Project |
Watch the video available at the link shown below
It summarises the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it |
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Spoken Tutorial Workshops |
The Spoken Tutorial Project Team
Conducts workshops using spoken tutorials Gives certificates to those who pass an online test For more details, please write to contact@spoken-tutorial.org |
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Acknowledgement |
Spoken Tutorial Project is a part of the Talk to a Teacher project
It is supported by the National Mission on Education through ICT, MHRD, Government of India More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro |
| The script has been contributed by FOSSEE and Spoken-tutorial team.
This is Ashwini Patil from IIT Bombay Thank You for joining. |
