#!/usr/bin/env perl
use strict;
use warnings;

my $num_files_to_write = 4;
use Data::Dumper;

my @filehandles; 
for my $id ( 1..$num_files_to_write ) {
   open ( my $fh, '>', "file_$id.txt" ) or die $!;
   push @filehandles, $fh; 
}

local $/ = '5';
while ( <> ) {
    select $filehandles[$. % $num_files_to_write];
    print; 
}

foreach my $fh ( @filehandles ) { 
   close ( $fh ); 
}