The values for configurable variables can be provided through configuration files, command-line arguments, and environment variables. The configuration values will be overridden in the following precedence order if the values are given through multiple ways when retrieving configurable values:

• Command-line arguments: The values can be configured through the command-line arguments when executing the Ballerina program. The configurable value provided through a command-line argument is expected to be the toString() representation of the intended value.

• Configuration files: The values can be configured through the configuration files in the TOML(v0.4) format. The file location can be specified through an environment variable with the name BAL_CONFIG_FILES. Ballerina supports specifying multiple configuration files using this environment variable with the OS-specific separator. The file precedence order will be as specified in the environment variable. If an environment variable is not specified, a file named Config.toml will be sought in the current working directory.
  Configuration values for testing can be provided in a file named Config.toml located in the tests directory. For more details, see Define test-specific configurations.

• Environment variables: Users can provide the configuration values through an environment variable with the name BAL_CONFIG_DATA in which the content is expected to be in the TOML(v0.4) format.

Note: Providing multiple configuration values through separate environment variables is not supported.

Provide via command-line arguments

The following syntax can be used to provide values for the variables through the command-line parameters:

-Ckey=value

Currently, the command-line based configuration is only supported for configurable variables of types int, byte, float, boolean, string, decimal, enum and xml.

The following examples explain the way of providing command-line arguments to configure variables of specific Ballerina types.

Ballerina type	Ballerina example	Command-line argument
boolean	configurable boolean isAdmin = ?;	bal run -- -CisAdmin=true or bal run -- -CisAdmin=1
int, byte	configurable byte age = ?; configurable int port = ?;	bal run -- -Cage=25 -Cport=9090
float, decimal	configurable float height = ?; configurable decimal salary = ?;	bal run -- -Cheight=5.6 -Csalary=50500.65
string	configurable string name = ?;	bal run -- -Cname=John
xml	configurable xml book = ?;	bal run -- -CxmlVar="<book>The Lost World</book>"
enum	enum Country { LK = "Sri Lanka", US = "United States" } configurable Country country = ?;	bal run -- -Ccountry="Sri Lanka"
union	configurable float|int|string measurement = ?;	bal run -- -Cmeasurement=5.0

Provide via TOML syntax

Ballerina defines a specific TOML syntax to be used when configuring the variables through the configuration files and environment variables. Depending on the type of the configurable variable, the way of providing values in the TOML content differs. Currently, TOML-based configuration is supported for configurable variables of int, float, boolean, string, xml, decimal, enum, the arrays of the respective types, map, record, table and the union of the respective types.

The mapping of Ballerina types to TOML types can be explained through the following examples:

Ballerina type	Ballerina example	TOML type	TOML example
nil	configurable string? city = "London"; type Address record { string? city = "Paris"; }; configurable Address address = {};	No TOML type is specified for the () value. A default value is expected when a configurable variable contains a nil type.
boolean	configurable boolean isAdmin = ?;	Boolean	isAdmin = true
int, byte	configurable byte age = ?; configurable int port = ?;	Integer	age = 25 port = 9090
float, decimal	configurable float height = ?; configurable decimal salary = ?;	Float	height = 5.6 salary = 50500.65
string	configurable string name = ?;	String	name = "John"
xml	configurable xml book = ?;	String	book = "<book>The Lost World</book>"
boolean[]	configurable boolean[] switches = ?;	Array of booleans	switches = [false, false, true]
int[] , byte[]	configurable int[] ports = ?;	Array of integers	ports = [9090, 9091]
float[], decimal[]	configurable float[] rates = ?;	Array of floats	rates = [55.4, 76.3, 38.5]
string[]	configurable string[] colors = ?;	Array of strings	colors = ["Red", "Green", "Blue"]
tuple	configurable [string, int, string[], map, int... ] student = ?;	Array of respective types	student = ["Jane", 1101, ["Maths", "English"], {level = 4, class = "B"}, 98, 76, 88]
map	configurable map <string> person = ?;	TOML table	[person] name = "Anna" city = "London"
map[]	configurable map <string>[] people = ?;	Array of TOML tables	[[people]] name = "John" city = "Paris" [[people]] name = "Jack" city = "Colombo"
record	type Person record { string name; int age; }; configurable Person person = ?;	TOML table	[person] name = "John" age = 45
record with record field	type Food record { string name; int cal; }; type Diet record { Food food; int age; }; configurable Diet input = ?;	TOML table - nested	[input] age = 20 food.name = "carrot" food.cal = 41
record[]	type Person record { string name; int age; }; configurable Person[] peope = ?;	Array of TOML tables	[[people]] name = "John" age = 45 [[people]] name = "Jack" age = 32
table	configurable table <map<string>> users = ?;	Array of TOML tables	[[users]] name = "Tom" occupation = "Software Engineer" [[users]] name = "Harry" occupation = "Doctor"
table[]	configurable table <map<string>>[] userTeams = ?;	2D Array of inline-TOML tables	userTeams = [[{name = "Tom", team = "Dev"}, {name = "Harry", team = "Dev"}], [{name = "Anna", team = "Finance"}]]
enum	enum Country { LK = "Sri Lanka" , US = "United States" } configurable Country country = ?;	String	country = "Sri Lanka"
union, anydata, json	configurable int|string code = ?; configurable anydata data = ?; configurable json payload = ?;	Relevant TOML type for the value	code = "10001A" data = 123 payload = {name = "Jane"}