mw55309,
Scalar::Util has looks_like_a_number. Here is the source:

sub looks_like_number {
  local $_ = shift;

  # checks from perlfaq4
  return 1 unless defined;
  return 1 if (/^[+-]?\d+$/); # is a +/- integer
  return 1 if (/^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/); # 
+a C float
  return 1 if ($] >= 5.008 and /^(Inf(inity)?|NaN)$/i) or ($] >= 5.006
+001 and /^Inf$/i);

  0;
}
[download]

As you can see, it handles the regex from the FAQ plus a few additional things.

Cheers - L~R