(untested)

@metrics=`cat a.txt`;
my %labels;
@labels[ 0 .. $#metrics ] = @metrics;
print $query->checkbox_group(-name=>'a',
                             -values=> [ 0 .. $#metrics ],
                             -labels=> \%labels,
                             -columns=> 1),
[download]

--
<http://www.dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg