The canonical answer to IsNan is found here: http://www.cpan.org/doc/FMTEYEWTK/is_numeric.html

To Quote: 

The special IEEE notions of Infinity and NaN (not a number) will be pr
+operly honored: 

  $n = 'NaN';
  print 2 * $n;
NaN
  print 10 * $n
NaN
  print 1 + NaN
NaN
  $i = 'Infinity' 
  print 1 + $i
Infinity
  print $i * $i
Infinity
  print $i - $i
NaN
  print 'Infinity' < 0
0
  print 'Infinity' > 0
1

[download]

hsm

Edit by tye to change very wide BLOCKQUOTE+PRE to CODE

In reply to Re: Checking whether a $var is a number by hsmyers
in thread Checking whether a $var is a number by George_Sherston

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