#!/usr/bin/perl -w
use strict;

my $dollar="100"; #test 1
#my $dollar="100.000"; #test 2
#my $dollar="10.000"; #test 3

my $amount= f_currency($dollar);

print "Testing=$amount\n";

sub f_currency {

my $num = shift @_;
my $number;

#make sure that the amount entering this sub has the decimal point followed by two numbers, if not dont go there. 
if($num=~/\d+\.\d{2}$/g) # This regular is not checking properly
 {
   $number = sprintf "%.2f", $num;
   # Add one comma each time through the do-nothing loop
   1 while $number =~ s/^(-?\d+)(\d\d\d)/$1,$2/;
   # Put the dollar sign in the right place
   $number =~ s/^(-?)/$1\$/;
    return $number;
}else{ #if the number dotn have the expected format just add the $ sign in front of it.
       $num="\$".$num;
       return $num;
       }

}