Interview › Scripting (Bash, Groovy)
What is an associative array, and how do you use one? [Intermediate]
Answer
An associative array is a Bash map from string keys to values. It is declared with declare -A and is useful for lookups such as service-to-port, environment-to-cluster, or counters by key.
Technical explanation
Associative arrays require Bash 4 or newer, so they are not available in old macOS system Bash 3.x unless a newer Bash is installed.
Use ${map[$key]} to read values and ${!map[@]} to iterate keys.
Under set -u, use ${map[$key]:-default} when a key might be absent.
Hands-on example
declare -A port_by_service=(
[api]=8080
[worker]=9090
)
svc="api"
echo "${svc} port is ${port_by_service[$svc]}"
for key in "${!port_by_service[@]}"; do
echo "$key -> ${port_by_service[$key]}"
done
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