Unless Config::Simple has special code to handle it, you shouldn't use "~" in your filename. When you use that from shell commands, it's the shell's job to expand it to your home directory, but it doesn't work in arbitrary filenames not expanded by the shell.

A quick fix would be to do my $rc_dir = glob("~"); and use $rc_dir, though something like use File::HomeDir; my $rc_dir = File::HomeDir->my_data; would be better.