/**
 * The error thrown when a required key is not found.
 */
export class EnvKeyNotFoundError extends Error {
    /**
     * Creates a new instance.
     * @param {string} key The key that wasn't found.
     */
    constructor(key: string);
    /**
     * The key that wasn't found.
     * @type {string}
     */
    key: string;
}
/**
 * The error thrown when a required key is present but is an empty string.
 */
export class EnvEmptyStringError extends Error {
    /**
     * Creates a new instance.
     * @param {string} key The key that wasn't found.
     */
    constructor(key: string);
    /**
     * The key that wasn't found.
     * @type {string}
     */
    key: string;
}
/**
 * A utility for interacting with environment variables
 *
 * @template {object} [T=Record<string, string|undefined>]
 */
export class Env<T extends object = Record<string, string | undefined>> {
    /**
     * Creates a new instance of Env.
     * @param {T} [source] The environment variable object to read from.
     */
    constructor(source?: T);
    /**
     * The object from which to read environment information.
     * @type {T}
     */
    source: T;
    /**
     * Retrieves an environment variable without checking for its presence.
     *
     * Returns a default value if the environment variable doesn't
     * exist.
     *
     * @overload
     * @param {string} key The environment variable name to retrieve.
     * @param {string|number|boolean} defaultValue The default value to return if the
     *      environment variable is not found.
     * @returns {string} The environment variable value if found or undefined if not.
     */
    get(key: string, defaultValue: string | number | boolean): string;
    /**
     * Retrieves an environment variable without checking for its presence.
     *
     * @overload
     * @param {string} key
     * @returns {string|undefined}
     */
    get(key: string): string | undefined;
    /**
     * Determines if a given environment variable exists.
     * @param {string} key The environment variable name to check.
     * @returns {boolean} True if the environment variable exists,
     *      false if not.
     */
    has(key: string): boolean;
    /**
     * Retrieves the first environment variable found in a list of environment
     * variable names.
     *
     * Returns a default value if the environment variable doesn't
     * exist.
     *
     * @overload
     * @param {string[]} keys The environment variable name to retrieve.
     * @param {string|number|boolean} defaultValue The default value to return if the
     *      environment variable is not found. Will be coerced to a string.
     * @returns {string} The environment variable value if found or undefined if not.
     * @throws {TypeError} If keys is not an array with at least one item.
     */
    first(keys: string[], defaultValue: string | number | boolean): string;
    /**
     * Retrieves the first environment variable found in a list of environment
     * variable names.
     *
     * @overload
     * @param {string[]} keys
     * @returns {string|undefined}
     * @throws {TypeError} If keys is not an array with at least one item.
     */
    first(keys: string[]): string | undefined;
    /**
     * Retrieves an environment variable. If the environment variable does
     * not exist or is an empty string, then it throws an error.
     * @param {string} key The environment variable name to retrieve.
     * @returns {string} The environment variable value.
     * @throws {Error} When the environment variable doesn't exist or is an
     *      empty string.
     */
    require(key: string): string;
    /**
     * Retrieves the first environment variable found in a list of environment
     * variable names and throws an error if none of the variables are found.
     * @param {string[]} keys An array of environment variable names.
     * @returns {string} The environment variable value.
     * @throws {TypeError} If keys is not an array with at least one item.
     * @throws {Error} When the environment variable doesn't exist or is an
     *      empty string.
     */
    requireFirst(keys: string[]): string;
    /**
     * Lazy-loading property containing a proxy that can be used to
     * automatically throw errors when an undefined environment variable
     * is accessed.
     * @returns {T} A proxy object.
     */
    get exists(): T;
    /**
     * Lazy-loading property containing a proxy that can be used to
     * automatically throw errors when an undefined or empty string
     * environment variable is accessed.
     * @returns {T} A proxy object.
     */
    get required(): T;
}
export namespace Env {
    export { EnvKeyNotFoundError as KeyNotFoundError };
    export { EnvEmptyStringError as EmptyStringError };
}