perldoc -m Scalar::Util::PP

sub looks_like_number {
  local $_ = shift;

  # checks from perlfaq4
  return 0 if !defined($_);
  if (ref($_)) {
    require overload;
    return overload::Overloaded($_) ? defined(0 + $_) : 0;
  }
  return 1 if (/^[+-]?[0-9]+$/); # is a +/- integer
  return 1 if (/^([+-]?)(?=[0-9]|\.[0-9])[0-9]*(\.[0-9]*)?([Ee]([+-]?[0-9]+))?$/); # a C float
  return 1 if ($] >= 5.008 and /^(Inf(inity)?|NaN)$/i) or ($] >= 5.006001 and /^Inf$/i);

  0;
}