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Bash Associative Array Cheat Sheet

Indexed Arrays in Bash

Unlike hashes indexed arrays require no declaration. Just assign values

# Assigning a fixed list
arr=("string 1", "string 2", "string 3")

# Pushing to an array
arr+=("new string value", "another new value")

# Assigning with indizes, allows sparse lists
arr=([1]="string 1", [2]="string 2", [4]="string 4")

# Adding single elements by index
arr[4]="string 4"

Indexed arrays are accessed the same way as “Hashes”. See below for accessing the different properties of an array.

Hashes in Bash

Associative arrays (aka hashes) can be used since Bash v4 and need a declaration like this

declare -A arr

After declaring the hash “arr” assign values like this

arr[my key]="my value"
arr["my key"]="my value"
arr[$my_key]="my value"

And access them like this

echo ${arr[my key]}
echo ${arr["my key"]}
echo ${arr[$my_key]}

Or check hash properties…

${arr[@]}         # Returns all indizes and their items (doesn't work with associative arrays)
${arr[*]}         # Returns all items
${!arr[*]}        # Returns all indizes
${#arr[*]}        # Number elements
${#arr[$n]}       # Length of $nth item

Delete an element (not that is unsafe and might not do what you want!)

undef arr[my key]

Iterating Bash Hashes

# Print = lines...
for k in "${!array[@]}"
do
  printf "%s\n" "$k=${array[$k]}"
done