Bash Array Reverse

Bash Array Reverse

In Bash scripting, reversing an array is useful for various tasks that require reversing the order of elements in an array.

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Syntax

reversed_array=()
for (( i=${#array[@]}-1; i>=0; i-- )); do
    reversed_array+=("${array[$i]}")
done

The basic syntax involves using a for loop to iterate over the elements of the array in reverse order and store them in a new array.

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Example Bash Array Reverse

Let's look at some examples of how to reverse an array in Bash:

1. Reverse an Array of Strings

This script initializes an array with string elements, reverses the array, and prints the reversed array.

#!/bin/bash

array=("element1" "element2" "element3")
reversed_array=()
for (( i=${#array[@]}-1; i>=0; i-- )); do
    reversed_array+=("${array[$i]}")
done
echo "Reversed array: ${reversed_array[@]}"

In this script, the array variable array is initialized with the elements 'element1', 'element2', and 'element3'. The for loop iterates over the elements of the array in reverse order, and the elements are stored in the reversed_array variable. The script then prints the reversed array.

2. Reverse an Array of Numbers

This script initializes an array with numeric elements, reverses the array, and prints the reversed array.

#!/bin/bash

array=(1 2 3)
reversed_array=()
for (( i=${#array[@]}-1; i>=0; i-- )); do
    reversed_array+=("${array[$i]}")
done
echo "Reversed array: ${reversed_array[@]}"

In this script, the array variable array is initialized with the elements 1, 2, and 3. The for loop iterates over the elements of the array in reverse order, and the elements are stored in the reversed_array variable. The script then prints the reversed array.

3. Reverse an Array with Elements from User Input

This script initializes an array with elements from user input, reverses the array, and prints the reversed array.

#!/bin/bash

array=()
while true; do
    read -p "Enter an element (or 'done' to finish): " element
    if [ "$element" == "done" ]; then
        break
    fi
    array+=("$element")
done
reversed_array=()
for (( i=${#array[@]}-1; i>=0; i-- )); do
    reversed_array+=("${array[$i]}")
done
echo "Reversed array: ${reversed_array[@]}"

In this script, the array variable array is initialized as an empty array using (). The user is prompted to enter elements, which are added to the array using the += operator. When the user types 'done', the loop exits. The for loop iterates over the elements of the array in reverse order, and the elements are stored in the reversed_array variable. The script then prints the reversed array.

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Conclusion

Reversing an array in Bash is a fundamental task for reversing the order of elements in an array in shell scripting. Understanding how to reverse arrays can help you manage and manipulate arrays effectively in your scripts.