Arrays are powerful data structures in Linux shell scripting that allow you to store and manage multiple values within a single variable efficiently.
Unlike simple scalar variables that hold only one value at a time, arrays organize collections of related data, making scripts more flexible and capable of handling complex tasks such as processing lists, managing configuration data, or batching commands.
Shell scripting supports both indexed arrays—where elements are accessed by numeric indices—and associative arrays—where elements are accessed by named keys.
Indexed Arrays
Indexed arrays use numeric indices starting at 0 by default. Elements can be assigned individually or collectively.
Declaration and Initialization:
declare -a indexed_array # Explicit declaration
indexed_array=(apple banana cherry) # Compound assignment
indexed_array[3]=date # Adding an element by indexAccessing Elements:
1. Access single element: ${indexed_array[1]} outputs "banana"
2. Access all elements: ${indexed_array[@]} or ${indexed_array[*]}
3. Length of array: ${#indexed_array[@]}
Example:
for element in "${indexed_array[@]}"; do
echo "Fruit: $element"
doneAssociative Arrays
Introduced in Bash 4, associative arrays allow elements to be accessed by arbitrary string keys rather than numeric indices.
Declaration and Initialization:
declare -A assoc_array # Declare an associative array
assoc_array=([name]="Alice" [role]="Developer" [location]="NY")
assoc_array[project]="Linux Mastery"Accessing Elements:
1. Access by key: ${assoc_array[name]} outputs "Alice"
2. Access all keys: ${!assoc_array[@]}
3. Access all values: ${assoc_array[@]}
4. Length: ${#assoc_array[@]}
Example:
for key in "${!assoc_array[@]}"; do
echo "$key: ${assoc_array[$key]}"
doneArray Manipulation Techniques
1. Adding Elements: Assign directly by index or key.
2. Updating Elements: Overwrite by reassigning values at indices or keys.
3. Deleting Elements: Use unset command (unset indexed_array[2], unset assoc_array[key])
4. Slicing Arrays: Extract parts of arrays using ${array[@]:start:length} syntax.
5. Searching: Using loops or utilities like grep on array contents.
6. Length Measurement: ${#array[@]} counts number of elements.
Iteration Patterns
Looping through arrays is essential for processing each element efficiently.
For Loop:
for element in "${indexed_array[@]}"; do
echo $element
doneIndex-based Loop:
for (( i=0; i<${#indexed_array[@]}; i++ )); do
echo "Index $i: ${indexed_array[i]}"
doneAssociative Array Loop:
for key in "${!assoc_array[@]}"; do
echo "$key: ${assoc_array[$key]}"
done.png)
