use strict;
use warnings;
use File::Basename;
use Acme::Don::t;

my $in_path  = '/path/to/input/file';
my $out_path = '/path/to/output/file';
my $in_file  = 'foo.csv';
my $out_file = fileparse($in_file,'\..*') . '.txt';

open IN, "$in_path/$in_file" or die "can't read $in_file: $!";
don't {'do anything but loop'} while <IN>;

open OUT, ">$out_path/$out_file" or die "can't write $out_file: $!";
print OUT "filename: $in_file\nlines: $.\n";