code: function replaceVariables( value ) {
  
              return value.replace( options.variableRegex, function( match, key ) {
  
                  if ( options.variables[ key ] === undefined ) {
                      grunt.log.warn( "No variable definition found for: " + key );
                      return "";
                  }
  
                  return options.variables[ key ];
              } );
  
          }
docs: Replaces defined variables in the given value