Arrays in Bash Shell

 

Creating and Using Arrays in Bash Shell Script

In Bash scripting, arrays are used to store multiple values in a single variable. Here's a step-by-step beginner-friendly explanation of how to create and use arrays.

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1. Declaring an Array

You can create an array by assigning values to it using parentheses () and separating the values with spaces.

Example:

my_array=(apple banana cherry)

Here:

• my_array is the name of the array.
• It stores three elements: "apple", "banana", and "cherry".

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2. Accessing Array Elements

Array elements are accessed using their index, starting from 0. You use the syntax ${array_name[index]} to access an element.

Example:

echo ${my_array[0]}  # Outputs: apple
echo ${my_array[1]}  # Outputs: banana
echo ${my_array[2]}  # Outputs: cherry

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3. Adding Elements to an Array

You can add a new element by assigning a value to a specific index.

Example:

my_array[3]="date"
echo ${my_array[3]}  # Outputs: date

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4. Displaying All Elements

To display all elements of the array, use @ or * inside the curly braces.

Example:

echo ${my_array[@]}  # Outputs: apple banana cherry date
echo ${my_array[*]}  # Outputs: apple banana cherry date

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5. Finding the Length of an Array

You can find the number of elements in the array using the syntax ${#array_name[@]}.

Example:

echo ${#my_array[@]}  # Outputs: 4

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6. Looping Through an Array

You can use a for loop to iterate over all elements in an array.

Example:

for item in "${my_array[@]}"; do
  echo $item
done

Output:

apple
banana
cherry
date

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7. Removing an Element

To remove an element, use the unset command followed by the array name and index.

Example:

unset my_array[1]
echo ${my_array[@]}  # Outputs: apple cherry date

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8. Replacing an Element

You can update the value of a specific index.

Example:

my_array[1]="blueberry"
echo ${my_array[@]}  # Outputs: apple blueberry cherry date

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9. Examples in Action

Here’s a complete script that demonstrates creating and using arrays:

Script:

#!/bin/bash

# Create an array
fruits=("apple" "banana" "cherry")

# Access elements
echo "First fruit: ${fruits[0]}"

# Add an element
fruits[3]="date"

# Display all elements
echo "All fruits: ${fruits[@]}"

# Find the length of the array
echo "Number of fruits: ${#fruits[@]}"

# Loop through the array
echo "Fruits list:"
for fruit in "${fruits[@]}"; do
  echo $fruit
done

# Remove an element
unset fruits[1]
echo "After removal: ${fruits[@]}"

# Replace an element
fruits[1]="blueberry"
echo "After replacement: ${fruits[@]}"

Key Points to Remember
Array indices start at 0.
Use ${array_name[index]} to access individual elements.
Use "${array_name[@]}" to access all elements.
Use ${#array_name[@]} to find the number of elements.