Oops!
--#--
OK, here's a flaw: Our match string accepts commas optionally, 
as long as they're aligned along the 3-digit boundaries. In 
other words, it'll match <i>999999,999</i> and <i>99999,999999999</i>
and so forth. But it won't accept <i>999,99,999</i>. <br>
<br>
You may decide to live with such a small thing, but before you do, consider 
the remedy.<br>
<br>
<code>
if ($string_to_test =~ 
	m/^\d{0,3},(\d{3},)*\d{3}(\.\d{2})?$|^\d*(\.\d{2})?$/) {
		do something here...
}
</code>
<br>
See that? We now have two alternate matching patterns, separated by the '|'
character. The second alternative is simple -- just digits. But note that the 
commas are <i>no longer optional</i> in the first alternative.<br>
<br>
What about negative numbers? Easy, add optional parentheses or a minus sign
(alternate matches again). Be sure to escape the minus and the opening and 
closing parentheses with backslashes.<br>
<br>
Enough. What next, names? Too easy. Let's do dates. <br>