-/* Substitutes $variables as defined by GETENV into INPUT and returns
- a copy of the resultant string. Supports $var and ${var} syntaxes;
- $$ substitutes as $. */
-char *
-fn_interp_vars (const char *input, const char *(*getenv) (const char *))
+
+/* Substitutes $variables as defined by GETENV into TARGET.
+ TARGET must be a string containing the text for which substitution
+ is required.
+ Supports $var and ${var} syntaxes;
+ $$ substitutes as $.
+*/
+void
+fn_interp_vars (struct string *target,
+ const char *(*getenv) (const char *))