#!/usr/bin/perl

use warnings;
use strict;

while (<DATA>) {
    chomp;
    my @line = split /,/;
    while (my @excerpt = splice(@line, 0, 3)) {
        print join(",", @excerpt), "\n";
    }
}
 
__DATA__
userid,application_id,time,userid,application_id,time,userid,application_id,tim
userid,application
,