Array in Bash Scripting | Bash Array Practicals with Example

Introduction

An array is one of the important concepts in Bash Scripting or Programming. Using arrays, we may store and retrieve elements in list form, which is useful for some applications. Additionally, arrays in bash enable us to write command-line programs for storing data in a list manner. Array in bash does not discriminate the string from a number, so an array can contain both strings and numbers.

Advantages

1. In an Array, we can store the multiple elements of different data types.
2. We can add or retrieve the array element based on the index number.
3. It solves the problem of creating a new variable for each value.

Disadvantages

1. Bash Scripting does not provide support for multi-dimensional arrays.
2. In another scripting or programming language, an array can contain another array but in bash, an array can’t store another array.

Declaration of an Array in Bash Scripting

Any variable can be used as an indexed array without having to declare it.

Use the keyword “declare” and the following syntax to explicitly declare a variable as a Bash Array:

declare -a array_name

Here,

array_name indicates the name of the array

In a Simple way, we can create an indexed array in the following form

array_name[index_num1]=value1
array_name[index_num2]=value2
array_name[index_num3]=value3
array_name[index_num4]=value4

Here,

index_num defined the positive index position of an array.

The index number starts from 0.

#!/bin/bash

## Creating an Indexed Array

declare -a emp_name

emp_name[0]="Alex"
emp_name[1]="Sam"
emp_name[2]="Roger"
emp_name[3]="Travis"

echo "${emp_name[@]}"

1) Creating Associative Arrays

The associative arrays are first declared, unlike numerically indexed arrays.

The associative arrays can be declared by using the keyword “declare” and the -A (uppercase) option. The syntax is as follows:

declare -a array_name

The method to create an associative array can be defined as:

declare -a array_name=(
array_name[index_num1]=value1
array_name[index_num2]=value2
array_name[index_num3]=value3
array_name[index_num4]=value4
)

For Example:

#!/bin/bash

## Creating an Indexed Array

declare -a sports=(
[0]=baseball
[1]=cricket
[2]=football
[3]=basketball
)

echo "${sports[@]}"

2) Initialization of an Array in Bash

To initialize an array in Bash, we can use the assignment operator(=), simply putting a list of the elements inside parenthesis and separating them with spaces.

#!/bin/bash

## Scripting the index of an array

declare -a company_name=("Welcome" "to" "BinFin Tech")

echo "${!company_name[@]}"

Accessing a Single Element from the Array

To access a single element from an array, use the index number inside the square brackets.

echo ${array_name[index]} 

Example:

#!/bin/bash

## Scripting the index of an array

declare -a company_name=("Welcome" "to" "BinFin Tech")

echo "${company_name[2]}"

Print the Bash Array

To print all the elements of a Bash Array together with their indices and details, we can use the keyword “declare” and the “-p” option. The following can be used to print the Bash Array:

#!/bin/bash

## Creating an Indexed Array

declare -a sports=(
[0]=baseball
[1]=cricket
[2]=football
[3]=basketball
)

declare -p sports

Operations performed on Array in Bash Scripting

A) Printing the keys of an Array

#!/bin/bash

## Scripting the index of an array

declare -a company_name=("Welcome" "to" "BinFin Tech")

echo "${!company_name[@]}"

echo "${company_name[2]}"

B) Printing the length of an Array

#!/bin/bash

## Length of the array

declare -a company_name=("Welcome" "to" "Bin" "Fin" "Tech")

echo "The length of the array is:" ${#company_name[@]}

echo "Array contain ${#company_name[@]} elements"

C) Loop through the Array

#!/bin/bash

company_name=(Welcome to BinFin Tech)

for i in "${company_name[@]}"

do 

echo "$i"

done

D) Adding Elements to an Array

#!/bin/bash

## Adding elements to an array

declare -a employee_name=("Alex" "Sam" "Roy" "Travis")

echo ${employee_name[@]}

employee_name[4]="Cooper"

echo "Adding an element in an array"

echo "${employee_name[@]}"

## Adding multiple elements in an array

employee_name+=("Maverick" "Dominic" "Flash")

echo "${employee_name[@]}"

E) Updating the element of an Array

#!/bin/bash

## Updating the element of an array

declare -a employee_name=("Alex" "Copper" "Sam")

echo ${employee_name[@]}

echo "After updating the array"

employee_name[2]="Sammy"

echo ${employee_name[@]}

F) Deleting an element from an Array

#!/bin/bash

## Delete an element in the array

declare -a employee_name=("Alex" "Sam" "Copper" "Travis")

echo ${employee_name[@]}

echo "After deleting an element in an array"

unset employee_name[1]

echo ${employee_name[@]}

echo ${!employee_name[@]}

G) Deleting the Entire Array

#!/bin/bash

## Delete an element in the array

## Deleting the entire array

declare -a employee_name=("Alex" "Sam" "Copper" "Travis")

echo "Before deleting an entire array"

echo ${#employee_name[@]}

unset employee_name

echo "After deleting an entire array"

echo ${#employee_name[@]}

H) Slicing the element of an Array

#!/bin/bash

## Slicing the array from index 1 to 5

declare -a employee=("Alex" "Sam" "Travis" "Copper" "Dominic" "Maverick")

for e in "${employee}"

do

echo "${employee[@]:1:5}"

done

Note: This blog is mainly referenced from the Javatpoint.

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