<?php

$fp = fopen("socket.zip", "rb");
$filesize = 10;
$i = 0;
$no = 1;
while(!feof($fp))
{
  $file = fread($fp, $filesize);

  $fp2 = fopen("./split/socket.port".sprintf("d",$no).".".$i."-".($i+$filesize).".tmp", "wb");
  fwrite($fp2, $file, $filesize);
  fclose($fp2);
  $i+=$filesize+1;
$no++;
}

fclose($fp);

<?php
$filelist = glob('./split/*socket*.tmp');
$filesize = 10;

//print_r($filelist);
$mergeFileName = 'merg.zip';

unlink($mergeFileName);
  $fp2 = fopen($mergeFileName,"w+");
foreach($filelist as $k => $v)
{
  $fp = fopen($v, "rb");
   $content = fread($fp, $filesize);

   fwrite($fp2, $content, $filesize);
   unset($content);
   fclose($fp);
   echo $k,"\n";
}
  fclose($fp2);