use strict;
use warnings;
$_ = 'This,is, an, example. Keep $2.50, 1,500, and 192.168.1.1.';
my @words = tokenize($_);
print join "|",@words;

######################################
sub tokenize   
######################################
{
 my $msg = shift;

 my $ntd = qr/(?<=\D)[,.]/;  
 my $dtn = qr/[,.](?=\D|$)/; 
 my $nv = qr/[^A-Za-z0-9\'\$!-.,]+/; 
 
 my %words;
 my @words = grep { !/^$/ and !$words{lc($_)}++} 
               split /$ntd|$dtn|$nv/,$msg;    
 return @words;
}   ##tokenize