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

More on Arrays in BASH

Learning Objectives

• Extract an element from an Array
• Replace an element in an Array
• Add an element to an Array
• Remove an element from an Array

Prerequisite

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You should be familiar with the Linux Operating System.

If not, for relevant tutorials please visit spoken hyphen tutorial dot org.

System Requirements

• Ubuntu Linux 12.04 OS and
• GNU Bash version 4.1.10

GNU Bash version 4 or above is recommended to practice this tutorial.

“Extract of element from an Array”

• Here, position is the index number.
• Note that index number always starts from zero

Syntax:

ArrayName[@]:position:Number of elements

ArrayName opening square bracket At sign closing square bracket colon position colon Number of elements to be extracted from the position mentioned.

gedit space array2.sh on the terminal.

#!/bin/bash

declare -a Linux=('Debian' 'Redhat' 'Ubuntu' 'Fedora')

• Debian,

• Redhat,
• Ubuntu and
• Fedora

The command

${Linux[@]:1:2}

will print two elements starting from index one which is Redhat.

First let's make the file executable by typingchmod space plus x space array2.sh .Press Enter.

dot slash array2.sh

Press Enter.

[Highlight]

Original elements in an array Linux: Debian Redhat Ubuntu Fedora

Original elements in the array Linux: Debian Redhat Ubuntu Fedora

[Highlight]

The two elements starting from index one(Redhat): Redhat Ubuntu

“Replace an element in an Array”

ArrayName[n]='NewWord'

ArrayName opening square bracket n closing square bracket equal to within single quote, NewWord.

Here 'n' is the index number or element number.

Linux[2]='Mandriva'

This command will replace the third element Ubuntu with Mandriva.

It says, as the script was already executed, we will not execute again, instead we will browse through its output as array2.sh is already executed.

We will switch to terminal and see the output.

All elements after replacement: Debian Redhat Mandriva Fedora

“Add an element to an Array”

Syntax:

ArrayName=("${ArrayName[@]}" "New_word_1" "New_word_2")

ArrayName equal to opening round bracket within double quote dollar symbol opening curly bracket ArrayName opening square bracket At sign closing square bracket closing curly bracket .

space within double quote New_Word_1 space within double quote New_Word_2 closing round bracket.

Switch to the code file.

Linux=("${Linux[@]}" "Suse")

Previously we had 4 elements, then we added 'Suse' and the end of the list making it total of 5 elements. The output is the list of all five elements

All elements After appending Suse: Debian Redhat Mandriva Fedora Suse

Remove an element from an Array

unset ArrayName[Index number]

Unset space ArrayName opening square bracket index number closing square bracket.

unset Linux[2]

And we will remove the third element Mandriva from the array Linux.

Here we have removed one element i.e. Mandriva making to count back to 4. The output will show the remaining list of elementsSwitch to terminal and observe the output

<PAUSE>

Summary

• Extract an element from an Array
• Replace an element in an Array
• Add element to an Array
• Remove element from an Array

Assignment

1. Declare an array names of length 7 and perform following operations

• extract three elements starting from index two
• Replace third element with 'XXX' and display all the elements
• Append any new name at the end of Array

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Acknowledgement

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This is Ashwini from IIT Bombay.

Thank you for joining.