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

##</code><code>##

###############################
sub token_2   
###############################
{
 my $msg = $string;
 my $ntd = qr/(?<=\D)[,.]|[,.](?=\D|$)|[^\w'\$!,.-]+/;
 our %words;
 @words{(split /$ntd/,$msg)} = ();
 return keys %words;
}   ## token2

##</code><code>##

################################
sub take_3
################################
{
 my $msg = $string;
 my %words;
 @words{$string =~
   m/(
      (?:
        (?:
           [\w'\$!-]|
           (?<=\d)[.,](?=\d)
        )
       )+
      )/gx}=();

 return keys %words;
}   ##take_3