[Term Entry] Command line Bash: Associative Arrays

content/command-line/concepts/bash/terms/associative-arrays/associative-arrays.md

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+---
+Title: 'Associative Arrays'
+Description: 'Stores and retrieves data using key-value pairs in Bash scripts'
+Subjects:
+  - 'Bash/Shell'
+  - 'Computer Science'
+Tags:
+  - 'Arrays'
+  - 'Bash/Shell'
+  - 'Data Structures'
+CatalogContent:
+  - 'learn-the-command-line'
+  - 'paths/computer-science'
+---
+
+**Associative arrays** in Bash are key-value pair [data structures](https://www.codecademy.com/resources/docs/general/data-structures) that allow users to store and retrieve values using unique keys instead of numeric indices. First introduced in Bash version 4, they provide a powerful way to organize and manipulate data in shell scripts.
+
+Associative arrays are particularly useful for creating lookup tables, storing configuration settings, counting occurrences, and organizing complex data in shell scripts. Their ability to use strings as indexes makes them more flexible than traditional indexed arrays when working with named data.
+
+## Syntax
+
+To work with associative arrays in Bash, we need to understand the following syntax elements:
+
+- `declare -A array_name`: Creates an empty associative array. The `-A` option is required to specify an associative array.
+- `array_name[key]=value`: Assigns a value to a specific key in the array.
+- `${array_name[key]}`: Retrieves the value associated with a specific key.
+- `${!array_name[@]}`: Returns all keys in the array.
+- `${array_name[@]}`: Returns all values in the array.
+- `unset array_name[key]`: Removes a specific key-value pair from the array.
+- `unset array_name`: Deletes the entire array.
+
+**Return value:**
+
+Associative arrays return the values associated with the specified keys when accessed.
+
+## Example 1: Creating and populating basic associative arrays
+
+The following example demonstrates how to declare and initialize an associative array in Bash:
+
+```bash
+# Declare an associative array
+declare -A user_details
+
+# Add key-value pairs
+user_details[name]="John Doe"
+user_details[email]="[email protected]"
+user_details[age]=30
+user_details[role]="Developer"
+
+# Print a specific value
+echo "Name: ${user_details[name]}"
+
+# Print all keys
+echo "Available information: ${!user_details[@]}"
+
+# Print all values
+echo "User details: ${user_details[@]}"
+```
+
+The output will be as follows:
+
+```shell
+Name: John Doe
+Available information: name email role age
+User details: John Doe [email protected] Developer 30
+```
+
+This example demonstrates the creation of an associative array called `user_details`, which stores various pieces of information about a user. The keys are strings (`'name'`, `'email'`, `'age'`, `'role'`), allowing access to specific values using those keys.
+
+## Example 2: Building a configuration manager with associative arrays
+
+Associative arrays are perfect for configuration management in Bash scripts. Here's how they can be used to store and retrieve application settings:
+
+```bash
+#!/bin/bash
+
+# Declare an associative array for configuration
+declare -A config
+
+# Load configuration values
+config[db_host]="localhost"
+config[db_port]="3306"
+config[db_user]="admin"
+config[db_name]="myapp"
+config[app_env]="development"
+config[debug]="true"
+config[log_level]="info"
+
+# Function to get configuration value
+get_config() {
+  local key=$1
+  local default_value=$2
+
+  # If the key exists in the array, return its value
+  if [[ -n "${config[$key]+x}" ]]; then
+    echo "${config[$key]}"
+  else
+    # Otherwise return the default value
+    echo "$default_value"
+    fi
+}
+
+# Usage examples
+echo "Database Host: $(get_config db_host)"
+echo "Log Level: $(get_config log_level 'warning')"
+echo "Cache Time: $(get_config cache_time '3600')"  # Doesn't exist, will use default
+
+# Check if debug mode is enabled
+if [[ "$(get_config debug)" == "true" ]]; then
+    echo "Debug mode is enabled"
+fi
+```
+
+The output will be as follows:
+
+```shell
+Database Host: localhost
+Log Level: info
+Cache Time: 3600
+Debug mode is enabled
+```
+
+This example demonstrates using an associative array to manage configuration settings. The `get_config` function retrieves values by key and provides default values for missing keys, making the configuration system robust and flexible.
+
+## Example 3: Creating a word frequency counter with associative arrays
+
+Associative arrays are excellent for counting and tracking occurrences. Here's how to build a simple word frequency counter:
+
+```bash
+#!/bin/bash
+
+# Declare an associative array for word counts
+declare -A word_counts
+
+# Sample text to analyze
+text="Bash scripting is powerful. Bash allows automation of repetitive tasks.
+Learn Bash to become more efficient at command line tasks."
+
+# Convert to lowercase and split into words
+for word in $(echo "$text" | tr '[:upper:]' '[:lower:]' | tr -d '.' | tr ' ' '\n'); do
+  # Skip empty words
+  if [[ -z "$word" ]]; then
+    continue
+  fi
+
+  # Increment the count for this word
+  if [[ -z "${word_counts[$word]}" ]]; then
+    word_counts[$word]=1
+  else
+    ((word_counts[$word]++))
+  fi
+done
+
+# Print the results
+echo "Word frequency analysis:"
+echo "-----------------------"
+
+# Sort words by frequency (highest first)
+for word in "${!word_counts[@]}"; do
+    echo "$word: ${word_counts[$word]}"
+done | sort -rn -k2
+```
+
+Output:
+
+```shell
+Word frequency analysis:
+-----------------------
+bash: 3
+to: 2
+tasks: 2
+powerful: 1
+of: 1
+more: 1
+line: 1
+learn: 1
+is: 1
+efficient: 1
+command: 1
+become: 1
+at: 1
+automation: 1
+allows: 1
+scripting: 1
+repetitive: 1
+```
+
+This example showcases how associative arrays can be used to count word frequencies in a text. The array keys are words, and the values are the number of occurrences. This pattern is commonly used in text processing and log analysis.
+
+To further enhance your Bash scripting skills, consider taking our [Learn Bash Scripting](https://www.codecademy.com/learn/bash-scripting) course.