my $convert = 0;
my $export = 0;
my $exportfile = "";
...

GetOptions(
    "convert"       => \$convert,
    "export"        => \$export,
    "exportfile=s"  => \$exportfile,
    "<>"            => \&badarg,
);
...

sub badarg
{
    my $badparm = $_[0];
    print"badarg $badparm\n";
}