$ perl -E ' use Scalar::Util qw{looks_like_number}; my @infs = (inf, Inf, INF, infinity, Infinity, INFINITY, -inf, -Inf, -INF, -infinity, -Infinity, -INFINITY, Inftyddssssd, infighting, Infighting, -Inftyddssssd, -infighting, -Infighting); say "$_ : ", looks_like_number($_) for @infs; ' inf : 20 Inf : 20 INF : 20 infinity : 20 Infinity : 20 INFINITY : 20 -inf : 28 -inf : 28 -inf : 28 -inf : 28 -inf : 28 -inf : 28 Inftyddssssd : 0 infighting : 0 Infighting : 0 -Inftyddssssd : 0 -infighting : 0 -Infighting : 0