I think that both the Cookbook and vroom miss some valid numbers.
Here's my proposed checker. HOpe I don't get wrong ones, instead :)
Roberto

#!/usr/bin/perl
     # check for numbers with punctuation

     use strict;

     # examples for "common-written" numbers 
     foreach my $var (

  '','foo 30','.20','20.',',20','20,','1.3E2', '2..3','++3','2.3.',
 ,'..3',  0,100,'100.23','1,100.23','-3E-2'
         
                      ) {
             print "String: $var\n";
             if (IsANumber($var)) {
                     print "vroom says True, ";
             } else {
                     print "vroom says False, ";
             }
             if (IsANumberCookbook($var)) {
                     print "Cookbook says True, ";
             } else {
                     print "Cookbook says False, ";
             }
             if (IsANumberMine($var)) {
                     my $out = $var * $var;
                     print "I say True and square is $out\n\n";
             } else {
                     print "I say False\n\n";
             }

     }

             
     sub IsANumber {

# vroom version

             my $var = $_[0];
             
             if (

               # contains digits,commas and 1 period
               ($var =~ /(^[0-9]{1,}?$)|(\,*?)|(\.{1})/) &&

               # does not contain alpha's, more than 1 period
               # commas or periods at the beggining and ends of
               # each line
               !($var =~ /([a-zA-Z])|(^[\.\,]|[\.\,]$)/) &&

               # is not null
               ($var ne '')

               ) { return(1) } 
               else { return(0) }
     }


     sub IsANumberCookbook {

# Perl Cookbook version

             my $var = $_[0];
             
             if (

                 $var =~ /^([+-]?)(?=\d|\.\d)\d*(\.\d)?([Ee]([+-]?\d+)
+)?$/

               ) { return(1) } 
               else { return(0) }
     }

     sub IsANumberMine {

# my version

             my $var = $_[0];
             
             if (

                 $var =~ /^([+-]?)(\d+\.|\.\d+|\d+)\d*([Ee]([+-]?\d+))
+?$/

               ) { return(1) } 
               else { return(0) }
     }
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