If you've got an international audience beware of dd/mm/yy versus mm/dd/yy formats which may make things more interesting.

No, that's not correct.

Besides the typos and the fact that you probably don't really want to eliminate whitespace or put non-date elements into your @dates array, your regex has some problems.

Working from the example you give, this might be a little closer to what you want:

my @dates;
while (<FILE>) { 
    while (m!(\d{2,4}[-/]\d{2}[-/]\d{2,4}|\w+\s+\d+\s+\d+)!g) {
        push @dates, "<date>$1</date>" 
    }
}
[download]

That could match a whole bunch of other stuff too though... If you can better explain what you need someone will almost surely give you something better than that.

-sauoq
"My two cents aren't worth a dime.";

Better explanation:
For example, if I have a file with the following:
2000-04-23 was a great day, but 04-24-1999 is much better.
The output should produce:
<date>2000-04-23</date> was a great day, but <date>04-24-1999</date> is much better. Since the dates could be something like 2000/04/23 I would like to match those 3 formats for now. Is this any better? Thanks for your help.

while ( <DATA> )
{
   s!\b((\d{4}[-/]\d{2}[-/]\d{2}\b)|(\d{2}[-/]\d{2}[-/]\d{4}))\b!<date
+>$1</date>!g;
   print;
}


__DATA__
2000-04-23 was a great day, but 04-24-1999 is much better.
2000/04/23 I would like to match those 3 formats for now.
2000-85-85 is not a real date.
[download]

The above regex does what you ask, but as noted by fellow monks, if you do not use a module, you will need to add other things to make sure what it is that you are matching is trully a date. As the above regex will accept 2000-73-08 which is not a valid date. One could write a regex to eliminate this possiblity, but as FamousLongAgo mentions there are vast subtleties as to what might be a valid date. (leap years, as one example,present a special problem). But then again only you know the data you are trying to match against.

As previously mentioned by saouq, if you give a better explanation of why don't want to use a module and what else you might need, someone will lead you in the right direction.