```{index} single: firstkey; Config function ``` ```{index} single: Config::firstkey; Perl function ``` # firstkey Tied-hash iterator: reset and return the first key. ## Synopsis ```perl my @keys = keys %Config; # triggers FIRSTKEY + NEXTKEY while (my ($k, $v) = each %Config) { ... } ``` ## What you get back The first key in the internal iteration order, or `undef` if the hash is empty. ## Edge cases - Iteration order is unspecified; never rely on it. - Calling `FIRSTKEY` resets a `NEXTKEY` walk in progress. ## Differences from upstream Fully compatible with upstream.