import { TransformFunc } from './types';
import { SubstitutionFunc } from '../types';
/**
 * A environment variable substitution transform that transforms e.g. 'token ${MY_TOKEN}'
 * to 'token abc' if MY_TOKEN is 'abc'. If any of the substituted variables are undefined,
 * the entire expression ends up undefined. Additionally, supports parameter substitution
 * syntax to provide a default or fallback value for a given environment variable if it is
 * unset; e.g. 'token ${MY_TOKEN:-xyz}' transforms to 'token xyz' if MY_TOKEN is unset.
 */
export declare function createSubstitutionTransform(env: SubstitutionFunc): TransformFunc;
