#!/usr/bin/perl
use strict;
use warnings;
use LWP::UserAgent;
use HTTP::Request;

my $ua = LWP::UserAgent->new;
open my $FILE, '<', 'clients.txt' or die "Open error: $!\n";
my @f = <$FILE>;
chomp @f;
close $FILE;
my ($req, $res, $content, $OUT);
my $url = 'http://site/cgi-bin/trstat.pl';
foreach my $name(@f) {
  $req = HTTP::Request->new (GET => $url . "?code=$name&month=2008-06");
  $req->content_type ('text/html');
  $res = $ua->request ($req);
  die "Can't get url $url: " . $res->status_line . "\n" unless $res->is_success;
  $content = $res->content;
  # тут, если нужно, производится парсинг полученного результата
  open $OUT, '>', $name . '.txt';
  print $OUT $content;
  close $OUT;
}