This might get the creative juices flowing. It does output as you'd expect, but there is a limitation in this sample. Namely, the '$predec' is empty and the '$postdec' is full when there is no decimal point in the number. Anyhow... just wanted to do something fun before lunch. If I was a REGEX guru (I'm not even close to that planet) I would think that a look-ahead/behind would be useful in this case.

Be kind, this is my first code post. :)

use strict;
use warnings;

my $precision = 4;
my $scale = 3;
my $regex = qr{\A(\d*?)\.?(\d*?)\z};

foreach my $float ("1", ".45", "3.452", "3.4526", "12.3", ".34567", "N
+aN") {
        if (my ($predec,$postdec) = ($float =~ m/$regex/)) {
                if (length "$postdec" > $scale) {
                        print "Invalid scale in $float ($predec\t$post
+dec)\n";
                } elsif (length "$predec" > $precision - $scale) {
                        print "Invalid precision in $float  ($predec\t
+$postdec)\n";
                }
                else {
                        print "Valid number: $float ($predec\t$postdec
+)\n";
                }
        } else {
                print "Invalid floating point number: $float\n";
        }
}
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