bruteforce

#!/usr/bin/perl
use warnings;
use strict;
my $loop = 1;
my @nums = (-10,-10,-10,-10);
my $idx = 0;
my $ecuation = $ARGV[0];
$ecuation =~ s/\_/**/g;
sub check{
        $ecuation =~ s/a/$_[0]/ge;
        $ecuation =~ s/b/$_[1]/ge;
        $ecuation =~ s/c/$_[2]/ge;
        $ecuation =~ s/d/$_[3]/ge;
        my @sides = split(/=/,$ecuation);
        if (eval($sides[0])==eval($sides[1])){
                print "a = $_[0] \nb = $_[1]\nc = $_[2]\nd = $_[3]\n";
                print "done..\n";
                exit;
        }
}
while($loop)
{
        &check(@nums);
        $idx = 0;
        $nums[$idx]++;
        while($nums[$idx]>10){
                $nums[$idx] = 0;
                $idx++;
                if($idx>4) {
                        $loop = 0;
                        last;
                }
                $nums[$idx]++;
        }