Split Mids to Several Lines With Fixed Number Per Line

We have many mids with one mid every line, now we want to print all those mids out with a fixed number of mids per line. I want to realize this function in Perl first without success, so I am using PHP.

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<?php

$scriptname = $argv[0];
$txt_file = $argv[1];
$dir = ".";

$contents = file_get_contents("$dir/$txt_file", FILE_USE_INCLUDE_PATH);
$contents = trim($contents);

$mid_splited = preg_split("/\n/", $contents);

$count_mids = count($mid_splited);

for ($i = 0; $i < $count_mids; $i++){
  print "$mid_splited[$i] ";
  if ($i % 7 == 0){
    print "\n";
  }
}


?>