my @data = (-123.004,-.008,0,-0,.0987,1.0,12345,'d','test');


foreach my $value (@data){
	
	$value = char_test($value);
	
	if ( $value =~/-?(\d?|\d+)\.?(\d?|\d+)/ && $value ne 'error' ){
		print "true\n";
	}
	else{
		print "false\n";
	}
}


sub char_test{
	my $value = shift;
	my @chars = $value =~/\D/g;
	
	foreach my $char (@chars){
		if ($char ne '-' && $char ne '.'){
			return 'error';
		}
	}
	return $value;
}

OUTPUT:
true
true
true
true
true
true
true
false
false