Associative arrays (declare -A) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an associative array in Bash?

An associative array in Bash is a collection of key-value pairs where keys are strings instead of numbers. It lets you store and access data using named keys.

beginner

How do you declare an associative array in Bash?

Use declare -A array_name to declare an associative array before using it.

beginner

How do you assign a value to a key in an associative array?

Use array_name[key]=value. For example, colors[apple]=red assigns 'red' to the key 'apple'.

beginner

How do you access a value from an associative array?

Use ${array_name[key]}. For example, ${colors[apple]} returns the value for the key 'apple'.

intermediate

How can you list all keys in an associative array?

Use ${!array_name[@]} to get all keys. For example, ${!colors[@]} lists all keys in the 'colors' array.

Which command declares an associative array named 'fruits' in Bash?

A declare -a fruits

B declare fruits

C array fruits

D declare -A fruits

Use declare -A to declare an associative array. declare -a is for indexed arrays.

How do you assign the value 'yellow' to the key 'banana' in an associative array named 'fruits'?

A fruits[banana]=yellow

B fruits["banana"]="yellow"

C fruits('banana')=yellow

D fruits{banana}=yellow

Keys and values with spaces or special characters should be quoted. The correct syntax is fruits["banana"]="yellow".

How do you print the value of the key 'apple' from the associative array 'fruits'?

A echo ${fruits[apple]}

B echo fruits[apple]

C echo ${fruits.apple}

D echo fruits(apple)

Use ${array_name[key]} to access values. So echo ${fruits[apple]} prints the value.

Which expression lists all keys of an associative array named 'fruits'?

A ${!fruits[@]}

B ${fruits[@]}

C ${fruits[*]}

D ${#fruits[@]}

${!fruits[@]} returns all keys. ${fruits[@]} returns all values.

What happens if you try to use an associative array without declaring it with declare -A?

A It works normally

B Bash treats it as an indexed array

C Bash throws an error

D It creates a string variable

Bash throws an error (e.g., 'must use subscript when assigning to an array') because non-numeric keys require declare -A for associative arrays.

Explain how to create and use an associative array in Bash with an example.

Think about how you name the array, add keys and values, and get values back.

Describe how to list all keys and all values from an associative array in Bash.

Remember the special syntax with exclamation mark for keys.