```{index} single: exists; Config function ``` ```{index} single: Config::exists; Perl function ``` # exists Tied-hash membership test: does a key exist in `%Config`? ## Synopsis ```perl if (exists $Config{useithreads}) { ... } ``` ## What you get back A true value when the key is part of the configuration (even if the recorded value is undef), false otherwise. ## Examples ```perl use Config; print exists $Config{d_fork} ? "yes" : "no"; # yes print exists $Config{nonesuch} ? "yes" : "no"; # no print exists $Config{useithreads} ? "yes" : "no"; # yes (value is undef) ``` ## Edge cases - Pair `EXISTS` with `FETCH` to distinguish "key is absent" from "key is present but undef". ## Differences from upstream Fully compatible with upstream.