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In this lesson, you’ll learn how to append elements to a Bash array and then sort that array using standard Unix utilities. We’ll cover:
  • Appending items with the += notation
  • Sorting array elements by printing each one on a new line
  • Capturing sorted output in a new array for easy comparison

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1. Appending Elements with +=

Bash arrays support the += operator to add one or more items at the end of an existing array. Here’s an example: 
#!/usr/bin/env bash
declare -a array=("One" "Two" "Three")
echo "Original array: ${array[@]}"

# Append three more elements
array+=("Four" "Five" "Six")
echo "After appending: ${array[@]}"
Save this as example2.sh and run: 
$ chmod +x example2.sh
$ ./example2.sh
Original array: One Two Three
After appending: One Two Three Four Five Six

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2. Sorting an Array with printf & sort

Bash doesn’t have a built-in array sort, but you can leverage the Unix sort command. Since sort expects one item per line, use printf to split space-separated elements:
Do not enclose each item in quotes (e.g., "a" "b"), or printf will treat them as single arguments and won’t split them into lines.
# Example: sorting letters
printf "%s\n" d a g h i f | sort
Output: 
a
d
f
g
h
i
You can apply the same method to numeric arrays: 
#!/usr/bin/env bash
declare -a nums=(4 2 0 6 8 1)

# Print each element on its own line and pipe to sort
printf "%s\n" "${nums[@]}" | sort
Running sort_numbers.sh: 
$ chmod +x sort_numbers.sh
$ ./sort_numbers.sh
0
1
2
4
6
8

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3. Displaying Unsorted and Sorted Arrays

To compare the original and sorted array side by side, capture the sorted output in a new array via command substitution: 
#!/usr/bin/env bash
declare -a nums=(4 2 0 6 8 1)

# Display the unsorted array
echo "Unsorted array: ${nums[@]}"

# Sort and capture in a new array
sorted_nums=($(printf "%s\n" "${nums[@]}" | sort))

# Display the sorted array
echo "Sorted array: ${sorted_nums[@]}"
Running sort_ex2.sh produces: 
$ chmod +x sort_ex2.sh
$ ./sort_ex2.sh
Unsorted array: 4 2 0 6 8 1
Sorted array: 0 1 2 4 6 8
The image shows a comparison between an unsorted array (4, 2, 0, 6, 8, 1) and its sorted version (0, 1, 2, 4, 6, 8) with a lightbulb icon above.

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Summary

TaskCommand Example
Append elementsarray+=("item1" "item2")
Sort an arrayprintf "%s\n" "${array[@]}" | sort
Capture sorted outputsorted=( $(printf "%s\n" "${array[@]}" | sort) )

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