use strict;
use warnings;
my $if = shift;
my ($of = $if) =~ s/\.csv$/.tab/ or die "usage: csv2tab file.csv";
open my $fh_i, "<", $if or die "$if: $!";
open my $fh_o, ">", $of or die "$of: $!";
my $csv = Text::CSV->new ({ binary => 1 });
my $tsv = Text::CSV->new ({ binary => 1, sep_char => "\t" });
while (my $row = $csv->getline ($fh_i)) {
    $tsv->print ($fh_o, $row);
    }
close $fh_i or die "$if: $!";
close $fh_o or die "$of: $!"