bash_array_cheatsheet.md

💻 Bash Array Cheat Sheet

🔢 Indexed Arrays (The Default Array)

Indexed arrays use non-negative integers (0, 1, 2, ...) as keys.

Section	Action	Syntax	Example
Declaration	Declare & Init	names=("Alice" "Bob" "Charlie")	Creates an array with keys 0, 1, 2.
Basics	Access Value	${names[1]}	Output: "Bob"
	All Values	${names[@]}	Output: "Alice Bob Charlie"
	All Keys	${!names[@]}	Output: "0 1 2"
	Count Elements	${#names[@]}	Output: 3
	Add/Set Element	names[3]="David"	Adds "David" at key 3.
	Remove Element	unset names[1]	Removes "Bob" and leaves a gap in the keys.
Looping	Loop Over Values	for name in "${names[@]}"; do echo "$name"; done	Outputs: Alice, Bob, Charlie (on new lines)
	Loop Over Keys	for i in "${!names[@]}"; do echo "Key $i: ${names[i]}"; done	Outputs: Key 0: Alice, Key 1: Bob, ...

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🔑 Associative Arrays (Key-Value Maps)

Associative arrays use strings as keys. They must be declared with declare -A.

Section	Action	Syntax	Example
Declaration	Declare & Init	declare -A config=(["host"]="server1" ["port"]=8080)	Creates an array mapping string keys to values.
Basics	Access Value	${config["host"]}	Output: "server1"
	All Values	${config[@]}	Output: "server1 8080"
	All Keys	${!config[@]}	Output: "host port"
	Count Elements	${#config[@]}	Output: 2
	Add/Set Element	config["user"]="admin"	Sets the value for the "user" key.
	Remove Element	unset config["port"]	Removes the "port" key and its value.
Looping	Loop Over Values	for value in "${config[@]}"; do echo "$value"; done	Outputs: server1, 8080 (on new lines)
	Loop Over Keys	for key in "${!config[@]}"; do echo "Key $key: ${config[$key]}"; done	Outputs: Key host: server1, Key port: 8080

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🔎 Associative Array Specific: Find Key by Value

# Example: Find the key whose value is "server1"
target_value="server1"
found_key=""

for key in "${!config[@]}"; do
    if [[ "${config[$key]}" == "$target_value" ]]; then
        found_key="$key"
        break
    fi
done

echo "Key for value '$target_value' is: $found_key"