🐚 Bash Arrays & Associative Arrays – arr=(), declare -A with Examples

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🧲 Introduction to Bash Arrays – Indexed and Associative Arrays Explained

In Bash scripting, arrays let you store multiple values in a single variable, making your scripts more efficient and organized. Bash supports two types of arrays:

• Indexed arrays – accessed by numeric indexes
• Associative arrays – accessed using string keys

While indexed arrays are available by default, associative arrays require explicit declaration using declare -A.

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🎯 In this article, you’ll learn:

• How to declare, access, and modify indexed arrays
• How to use associative arrays with string keys
• Syntax differences between the two array types
• Real-world examples and best practices

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📦 What Are Arrays in Bash?

Arrays in Bash allow you to group related data together. Instead of using separate variables like val1, val2, val3, you can group them as:

arr=(val1 val2 val3)

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📋 Indexed Arrays – Syntax and Usage

✅ Declare an Indexed Array

fruits=("apple" "banana" "cherry")

🧾 Access Elements

echo ${fruits[0]}  # Output: apple
echo ${fruits[1]}  # Output: banana

🛠️ Add or Update Elements

fruits[3]="orange"
fruits[1]="mango"

📌 Loop Through Array

for fruit in "${fruits[@]}"; do
  echo "$fruit"
done

📊 Get Array Length

echo ${#fruits[@]}  # Number of elements

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🧠 Associative Arrays – Key-Value Storage

✅ Declare an Associative Array

declare -A capitals

🧾 Add Elements

capitals[India]="New Delhi"
capitals[France]="Paris"
capitals[Japan]="Tokyo"

🔍 Access Elements

echo ${capitals[India]}  # Output: New Delhi

📌 Loop Through Keys

for country in "${!capitals[@]}"; do
  echo "$country: ${capitals[$country]}"
done

📊 Get All Keys or Values

echo "${!capitals[@]}"  # Keys
echo "${capitals[@]}"   # Values

⚠️ Associative arrays require Bash version 4.0+ and must be declared using declare -A.

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🧪 Example: Student Grades (Associative Array)

declare -A grades
grades[Alice]=95
grades[Bob]=88
grades[Charlie]=78

for student in "${!grades[@]}"; do
  echo "$student scored ${grades[$student]}"
done

✅ Output:

Alice scored 95
Bob scored 88
Charlie scored 78

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🚫 Common Mistakes to Avoid

Mistake	Fix
Accessing undeclared associative array	Use declare -A first
Using unquoted variables in loops	Always quote "${array[@]}"
Trying associative arrays in Bash < 4	Upgrade or avoid declare -A

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📌 Summary – Bash Arrays & Associative Arrays

Arrays bring structure and efficiency to Bash scripts. Use indexed arrays for ordered lists, and associative arrays when you need key-value mappings. Mastering both allows you to build advanced CLI tools and automate complex logic.

🔍 Key Takeaways:

• Use arr=(...) for indexed arrays
• Use declare -A arr for associative arrays
• Use "${arr[@]}" for safe iteration
• Associative arrays require Bash 4+

⚙️ Real-world Uses:

• Manage user-role pairs
• Store filename-extension mappings
• Track counts, totals, or states in scripts

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❓ FAQ – Bash Arrays & Associative Arrays

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❓ How do I check the length of a Bash array?
✅ Use:

echo ${#array[@]}

This returns the number of elements.

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❓ Can Bash arrays be multi-dimensional?
✅ No native support, but you can simulate with naming conventions or indexed keys:

matrix[0,0]=1

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❓ Are associative arrays supported in all Bash versions?
✅ No. Associative arrays are supported only in Bash 4.0 or newer.

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❓ How do I loop through both keys and values in associative arrays?
✅ Use:

for key in "${!arr[@]}"; do
  echo "$key: ${arr[$key]}"
done

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❓ What’s the safest way to loop through an array with spaces?
✅ Always quote:

for val in "${array[@]}"; do echo "$val"; done

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