use Getopt::Long qw(GetOptions);

GetOptions('in=s') or die;

$txt = $opt_in . ".txt";

$aspx = $opt_in . ".tab" . ".aspx";

open (TXT, "< $txt") || die;

...

close(TXT)

open (ASPX, "< $aspx") || die;

...

close(ASPX)