Difference between revisions of "BASH/C2/More-on-Loops/English"

Nested for loop in BASH

• Nested for loop
• With the help of an example

• Ubuntu Linux 12.04 Operating System and
• GNU BASH version 4.1.10

Please note, GNU Bash version 4 or above is recommended to practise this tutorial.

you should be familiar with arrays and loops in Bash.

For relevant tutorials, please visit our website:

http://spoken-tutorial.org

A loop within a loop is known as nested loop.

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

Double-click to open simple-nested-for directory

Here is a directory on the Desktop named simple-nested-for. Let's open it.

In each sub-directory there are multiple text files.

This program displays all the files within each subdirectory.

Please note that the same can be acheived with a single line command

ls -1 -R test*

But we will do it using a for-loop.

#!/usr/bin/env bash

for dir in test*; do

echo "Files in $dir directory:"

echo " "

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.

It will check for files present within the directories.

ls displays the directory content.

-1 is used to list one file per line.

done

echo "------------------------"

done

'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.

Ctrl+alt+t

Open the terminal by pressing ctrl+alt+t keys simultaneously on your keyboard.

chmod +x nested-for.sh

./nested-forsh

chmod +x nested-for.sh

Type:

./nested-for.sh

Output

It shows

• Files in test directory.
• Files in test2 directory.
• And files in test3 directory.

Let us summarize.

Summary

In this tutorial we learnt,

Nested for loop

Assignment

Retype the above program using nested while loop.

Save your program with the name 'nested-while.sh'

http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial

About the Spoken Tutorial Project

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Acknowledgement

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

This is Ashwini Patil from IIT Bombay

Thank You for joining.