refactor: use name normalizing function + sed for env vars

Add a function to "normalize" the name of config options that will be
used, while using sed instead of grep to both retrieve and manipulate
the names of environment variables that start with MUMBLE_CONFIG_.

entrypoint.sh

@@ -9,19 +9,22 @@ readonly CONFIG_REGEX="^(\;|\#)?\ *([a-zA-Z_0-9]+)=.*"
 # Compile list of configuration options from the bare-bones config
 readarray -t existing_config_options < <(sed -En "s/$CONFIG_REGEX/\2/p" "$BARE_BONES_CONFIG_FILE")
 
+# Grab the original command line that is supposed to start the Mumble server
+declare -a server_invocation=("${@}")
+declare -a used_configs
+
+normalize_name() {
+	local uppercase="${1^^}"
+	echo "${uppercase//_/}"
+}
+
 # Create an associative array for faster config option lookup
 declare -A option_for
 
 for config in "${existing_config_options[@]}"; do
-	# Ignore underscores during lookup
-	no_underscores="${config//_/}"
-	option_for["${no_underscores^^}"]="$config"
+	option_for["$(normalize_name "$config")"]="$config"
 done
 
-# Grab the original command line that is supposed to start the Mumble server
-declare -a server_invocation=("${@}")
-declare -a used_configs
-
 array_contains() {
 	local array_expansion="$1[@]" seeking="$2"
 	for element in "${!array_expansion}"; do
@@ -63,9 +66,7 @@ else
 	# Process settings through variables of format MUMBLE_CONFIG_*
 
 	while IFS='=' read -d '' -r var value; do
-		# Uppercase and remove underscores so MUMBLE_CONFIG_A_B == MUMBLE_CONFIG_AB
-		uppercase_variable="${var/MUMBLE_CONFIG_/}"
-		config_option="${option_for[${uppercase_variable//_/}]}"
+		config_option="${option_for[$(normalize_name "$var")]}"
 
 		if [[ -z "$config_option" ]]; then
 			>&2 echo "[ERROR]: Unable to find config corresponding to variable \"$var\""
@@ -73,7 +74,8 @@ else
 		fi
 
 		set_config "$config_option" "$value"
-	done < <( printenv --null | grep -az MUMBLE_CONFIG_ ) # Feeding it in like this, prevents the creation of a subshell for the while-loop
+	done < <( printenv --null | sed -zn 's/^MUMBLE_CONFIG_//p' )
+	# ^ Feeding it in like this, prevents the creation of a subshell for the while-loop
 
 	# Apply default settings if they're missing