option_replacement( "tar=s", sub { system "tar xf $_[1] -C $tmpdir"; "$tmpdir/*" } );

##</code><code>##

use Getopt::Long;
sub option_replacement
{
	my( $spec, $func ) = @_;
	local $Getopt::Long::passthrough=1;
	my @newARGV;
	GetOptions(
		$spec => sub { push @newARGV, &$func },
		'<>'  => sub { push @newARGV, @_ },
	);
	@ARGV = @newARGV;
}