sub usage
{
    my $err = shift and select STDERR;
    print "usage: $0 [--options] ...\n";
    exit $err;
    } # usage

use Getopt::Long qw(:config bundling);
my $opt_v = 0;
GetOptions (
    "help|?"      => sub { usage (0); } # OK, STDOUT
    "v|verbose:1" => \$opt_v,
    "x|xfsgdft!"  => \my $opt_x,
    ) or usage (1); # FAIL: STDERR


##</code><code>##

> some_app --help |& less


##</code><code>##

$ perl foo.pl big_file.txt >excerpt.csv
Opening file …
Analyzing columns …
Validating data …
Generating CSV … 1 2 3 4 5
Done!
$