It seems like you got it all down - so where is your question ?

I'll employ Psi::ESP and try to guess - you want to know how to check that a scalar contains a string that can be interpreted as a valid number - this is easy, as long as your definition of "number" is sane.

As you're talking about "price", I guess that your convention of "number" is "at least one digit from the range of 0 to 9, possibly followed by more such digits, possibly followed by a dot (to delimit the decimals), and then, if there was a dot, two more digits from the range 0 to 9".

After you've accepted this definition or have come up with your own definition, we need to translate this definition into a regular expression, since that's the easiest way of doing such things like conformance checks, as soon as you know regular expressions :

my $price = "100.09";

if ($price =~ / ^      # We begin at the start of the string
                [0-9]+ # At least one digit, possibly followed by more
                (      # Then (possibly, see below) follows
                  \.   # a dot
                  [0-9][0-9] # and two more digits
                )?     # But the decimal part is optional
                $      # And that's all there is to be
              /x) {

} elsif {
  die "'$price' dosen't look like a valid price.\n"
};
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Update: Please do note that my guessed definition of "number" differs at least from BUUs definition of "number" below. It's not hard to come up with a solution that includes BUUs definition as well, but personally, I think a number should ALWAYS start with a digit from the range 0 to 9.

To add a support for the weird definition which allows a number to start with a period, use the following RE :

  /^([0-9]+(\.[0-9]{2})?)|(\.[0-9]{2})$/
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perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
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For the sake of completness, we should also throw in numbers that start with a comma ",". Much of continental europe use number of the form 123 456,789 to be what we would normally right as 123,456.789

Of course, if the number supplying audience includes a few mathematicians or science types, we might also encounter numbers such e^12 (where e=2.718... (or somethng)).

Only problem is it fails on ".23" =[

The logical answer there is to do:


/^\d*(\.\d\d)?$/;
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but of course that matches litterally everything. So good luck

One way to do this would be:

my $price = "123.45";

if ($price =~ m/^\d*\.\d{2}$/) { .. }
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For more pattern matching related questions please read the perlre manpage..

Regards, -octo

Doing a search for "currency validation" came up with one useful question that had already been asked: integer validation.

You could also look at Params::Validate or CGI::Validate.

   my $price = $some_price_formatted_like_above;
   if ($price =~ /\d+[.,]?\d*|[.,]\d+/) {...}
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