static int escape(struct ast_channel *chan, char *cmd, char *data, char *buf, size_t len)
{
  AST_DECLARE_APP_ARGS(args,
                       AST_APP_ARG(escaped);
                       AST_APP_ARG(string);
                       );
  AST_STANDARD_APP_ARGS(args, data);

  if (!args.string) {
    ast_log(LOG_ERROR, "Usage: ESCAPE(<escape-chars>|<string>)\n");
    return -1;
  }

  char *bufptr = buf;
  int strlength = strlen(args.string),  escplength = strlen(args.escaped), a = 0, b = 0;

  ast_log(LOG_DEBUG, "Characters to escape: (%s)\n", args.escaped);
  ast_log(LOG_DEBUG, "String to escape: (%s)\n", args.string);

  for (a = 0; a < strlength; a++) {
    for (b = 0; b < escplength; b++) {
      if ( args.string[a] == args.escaped[b]) {
        *bufptr++ = '\\';
      }
    }
    *bufptr++ = args.string[a];
  }

  *bufptr = '\0';
  return 0;
}

static struct ast_custom_function escape_function = {
  .name = "ESCAPE",
  .synopsis = "Escapes characters in a given string",
  .syntax = "ESCAPE(<escape-chars>|<string>)",
  .read = escape,
};


res |= ast_custom_function_unregister(&escape_function);

res |= ast_custom_function_register(&escape_function);