}
bool on_tty(void) {
+
+ /* We check both stdout and stderr, so that situations where pipes on the shell are used are reliably
+ * recognized, regardless if only the output or the errors are piped to some place. Since on_tty() is generally
+ * used to default to a safer, non-interactive, non-color mode of operation it's probably good to be defensive
+ * here, and check for both. Note that we don't check for STDIN_FILENO, because it should fine to use fancy
+ * terminal functionality when outputting stuff, even if the input is piped to us. */
+
if (cached_on_tty < 0)
- cached_on_tty = isatty(STDOUT_FILENO) > 0;
+ cached_on_tty =
+ isatty(STDOUT_FILENO) > 0 &&
+ isatty(STDERR_FILENO) > 0;
return cached_on_tty;
}