Create dictionaries or maps in Bash

bash 4.0 natively supports creating hash tables / maps / dictionaries.

Using maps in Bash

Variables in bash are loosely typed; however, declaring provides a type-like behavior. One of the supported types in bash is an associative array (-A).

To declare an associative array:

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declare -A scores

To declare and instantiate in a single line:

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declare -A scores=( ["peter"]=95 ["sally"]=98 )

Add key/value pairs

Adding key/value pairs to an existing associate array:

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scores["tom"]=85

# using variables
name="brandon"
score=50
scores[$name]=$score

Retrieve key/value pairs

Retrieving key/value pairs from an existing associative array:

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name="peter"
echo ${scores[$name]} # 95

Update an existing key/value pair

Updating an existing key/value pair in an existing associative array:

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name="peter"
scores[$name]=100
echo ${scores[$name]} # 100

Check if a key exists

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name="peter"
if [ -v scores[$name] ]; then
    echo "$name exists in the map"
fi
# Output: peter exists in the map

Remove a key

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name="peter"
unset scores[$name]

Iterate map

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

Output:

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tom 85
brandon 50
sally 98
peter 100