> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Bash Array
A Bash array is a one-dimensional data structure capable of storing multiple values under a single variable identifier. Bash supports two types of arrays: **indexed arrays**, which use zero-based integers as keys, and **associative arrays** (introduced in Bash 4.0), which use arbitrary strings as keys. Bash arrays are dynamically sized, mutable, and do not require contiguous memory allocation.
## Declaration and Initialization
**Indexed Arrays**
Indexed arrays can be declared explicitly using the `declare` built-in or implicitly through assignment.
```bash theme={"dark"}
# Explicit declaration
declare -a my_indexed_array
# Implicit declaration via compound assignment
my_indexed_array=(value0 value1 value2)
# Sparse assignment (indices do not need to be sequential)
my_indexed_array[0]="first"
my_indexed_array[5]="sixth"
```
**Associative Arrays**
Associative arrays must be explicitly declared using the `-A` flag before they can be initialized or used.
```bash theme={"dark"}
# Explicit declaration (mandatory)
declare -A my_assoc_array
# Compound assignment
my_assoc_array=([key1]="value1" [key2]="value2")
# Individual assignment
my_assoc_array[key3]="value3"
```
## Accessing Elements
Accessing array elements requires parameter expansion using curly braces `{}` to prevent the shell from interpreting the index brackets as literal characters.
```bash theme={"dark"}
# Access a specific element
echo "${my_indexed_array[0]}"
echo "${my_assoc_array[key1]}"
# Access all elements
echo "${my_indexed_array[@]}"
echo "${my_indexed_array[*]}"
```
*Note on Expansion:* When enclosed in double quotes, `"${array[@]}"` expands each element as a separate word, preserving whitespace within elements. `"${array[*]}"` expands all elements into a single word, separated by the first character of the `IFS` (Internal Field Separator) variable.
## Modifying Arrays
**Appending Elements**
The `+=` operator appends elements to an indexed array without requiring knowledge of the current highest index.
```bash theme={"dark"}
# Append multiple elements
my_indexed_array+=(value3 value4)
# Append to an associative array
my_assoc_array+=([key4]="value4")
```
**Deleting Elements**
The `unset` built-in removes specific elements or the entire array from memory.
```bash theme={"dark"}
# Delete a specific element (creates a sparse array)
unset 'my_indexed_array[1]'
unset 'my_assoc_array[key1]'
# Delete the entire array
unset my_indexed_array
```
## Array Metadata
Bash provides specific parameter expansion syntax to retrieve metadata about the array, such as its size or its keys.
```bash theme={"dark"}
# Get the total number of elements in the array
length="${#my_indexed_array[@]}"
# Get the string length of a specific element
elem_length="${#my_indexed_array[0]}"
# Get all keys/indices currently in use
indices=("${!my_indexed_array[@]}")
keys=("${!my_assoc_array[@]}")
```
## Array Slicing
Indexed arrays support slicing via parameter expansion, allowing extraction of a subset of elements based on an offset and length.
```bash theme={"dark"}
# Syntax: ${array[@]:offset:length}
# Extract 2 elements starting from index 1
slice=("${my_indexed_array[@]:1:2}")
```
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