This code snippet contains a bug free(R) expression allowing you to parse D20 notation dice, so you can parse strings like 3D6,3D6+4 and 3D6+4x1000 obtaining as result (for 3D6+4x1000):
$dtime = 3
$dface = 6
$addfact = 4
$mulfact = 1000
The snippet set also right default value is a field is missing, so you can use returned value directly for calculation 
#!/usr/bin/perl -w 
use strict;
my @sample=("3D6+","3D6","3D6+4","3D6+4x1000");
##############################THE BIG, THE ONE
my $rexp='^([1-9][0-9]*)[Dd]([1-9][0-9]*)(\+([1-9][0-9]*)(x([1-9][0-9]
+*))?)?$';
my ($dtime,$dface,$foo,$addfact,$bar,$mulfact);
foreach (@sample)
{
    if (/$rexp/)
    {
        map{$_=0 if !defined($_)}($dtime,$dface,$foo,$addfact,$bar)=($
+1,$2,$3,$4,$5);
        $mulfact=(!defined($6))?1:$6;
        print "$_ is $dtime dices with $dface faces plus $addfact all 
+mult by $mulfact\n";
    }
}

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In reply to D20 dice throw parser by Luca Benini

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