my $cypher; if (eval { require Crypt::Twofish }) { $cypher = 'Crypt::Twofish'; } elsif (eval { require Crypt::Twofish_PP }) { warn("Crypt::Twofish not found. Falling back to slower Crypt::Twofish_PP\n") if $DEBUG; $cypher = 'Crypt::Twofish_PP'; } else { die("Neither Crypt::Twofish nor Crypt::Twofish_PP was found. Aborting"); }