import { TimeSpan } from '../conversion/TimeSpan';
/**
 * Returns whether the specified environment variable is defined.\
 * **NOTE**: Even if the variable is assigned a value of '', it is considered defined.
 * @param name The name of the variable to test.
 * @returns true if the variable is defined; false otherwise.
 */
export declare function isVariableDefined(name: string): boolean;
/**
 * Gets the value of the specified environment variable.  If the environment variable is not defined,
 * the behavior depends on whether a defaultValue parameter is provided:
 * - If defaultValue is provided, that value is returned.
 * - If defaultValue is not provided, a [[MissingEnvironmentVariableError]] is thrown.
 * @param name The name of the environment variable to retrieve.
 * @param defaultValue The value to be returned if the requested environment variable does not exist.
 * @returns The value of the requested environment variable or defaultValue.
 * @throws [[MissingEnvironmentVariableError]] if the requested environment variable is not defined
 *                                             and defaultValue is not provided.
 */
export declare function getVariable(name: string, defaultValue?: string): string;
/**
 * Gets the value of the specified environment variable as a boolean.  If the environment variable is not
 * defined, the behavior depends on whether a defaultValue parameter is provided:
 * - If defaultValue is provided, that value is returned.
 * - If defaultValue is not provided, a [[MissingEnvironmentVariableError]] is thrown.
 * @param name The name of the environment variable to retrieve.
 * @param defaultValue The value to be returned if the requested environment variable does not exist.
 * @returns The value of the requested environment variable or defaultValue.
 * @throws [[MissingEnvironmentVariableError]] if the requested environment variable is not defined and
 *                                             defaultValue is not provided.
 * @throws [[InvalidEnvironmentVariableError]] if the environment variable exists, but cannot be converted
 *                                             to a boolean.
 */
export declare function getVariableAsBoolean(name: string, defaultValue?: boolean): boolean;
/**
 * Gets the value of the specified environment variable as a number.  If the environment variable is not
 * defined, the behavior depends on whether a defaultValue parameter is provided:\
 * - If defaultValue is provided, that value is returned.\
 * - If defaultValue is not provided, a [[MissingEnvironmentVariableError]] is thrown.
 * @param name The name of the environment variable to retrieve.
 * @param defaultValue The value to be returned if the requested environment variable does not exist.
 * @returns The value of the requested environment variable or defaultValue.
 * @throws [[MissingEnvironmentVariableError]] if the requested environment variable is not defined and
 *                                             defaultValue is not provided.
 * @throws [[InvalidEnvironmentVariableError]] if the environment variable exists, but cannot be converted
 *                                             to a number.
 */
export declare function getVariableAsNumber(name: string, defaultValue?: number): number;
/**
 * Gets the value of the specified environment variable as a [[TimeSpan]].
 * @param name The name of the environment variable to retrieve.
 * @param defaultValue The value to be returned if the requested environment variable does not exist.
 * @returns The value of the requested environment variable or defaultValue.
 * @throws [[MissingEnvironmentVariableError]] if the requested environment variable is not defined and
 *                                             defaultValue is not provided.
 * @throws [[InvalidEnvironmentVariableError]] if the environment variable exists, but cannot be converted
 *                                             to a TimeSpan.
 */
export declare function getVariableAsTimeSpan(name: string, defaultValue?: TimeSpan): TimeSpan;