#!/usr/bin/perl

use strict;
use warnings;

my $sep=","; 
open (my $csv_file , "<" , 'csvfile.csv');
open (my $tab_file , ">" , 'tabfile.tab');
while(<$csv_file>) { 
   s/\Q$sep\E/\t/g; 
   print $tab_file, $_;
 } 
warn "Changed $sep to tab on $. lines\n"