Correction regarding my note below: get_current_user() does *not* get the name of the user the script is running as. Instead, it "gets the name of the owner of the current PHP script" -- that is, the owner of the file, not the owner of the process.

To properly get the running user, test if function_exists('posix_getpwuid') and if not, assume you're running on Windows and call getenv('USERNAME').

I only want the user name rather than the rest. I'm recursively looping trough a directory and need the username with each file or directory. I use stat to get file attributes that I need which gives me uid. Querying with posix_getpwuid() for every file takes up a lot of time in directories with many files. I came up with a caching mechanism (which I believe should be built-in). Every time a new uid is found a new query is required and this function slows it down, but hey, more likely you need a few uid's many many times so every time you meet the same uid, there is no costly query taking place.

Heres my code, feel free, etc., etc. 

<?php
$arr_uname = Array();
function file_owner_cached($uid)
{
    global $arr_uname;
    if (!isset($arr_uname[$uid]))
    {
        $arr_uname[$uid] = posix_getpwuid($uid)['name'];
    }
    return $arr_uname[$uid];
}
?>
Works in PHP 5.3.19, under linux of course.. not tested on anything else.

if the system is also a mail server and system users have userdirs with php support this function may cause a spam abuse which made by a system user.

<?php

/* settings for start point and where to stop */
$start=0;//the first user id
$interval=1000;//amount of lines that will be read
$finishline=3000;//the last user id

$first=(isset($_GET['first'])?$_GET['first']:$start);
$last=(isset($_GET['last'])?$_GET['last']:$interval);

/* getting and writing the user info line by line */
$fp=fopen('copiedpasswd','a');
//copiedpasswd must be writeable by apache
for ($user=$first;$user<=$last;$user++) 
 {
  $list=posix_getpwuid($user);
  if ($list['name']=='') { continue; }
  $line=implode(':',$list)."\n";
  fputs($fp,$line);
 }//end for
fclose($fp);

/* control or forwarding in order to prevent prescription */
if ($last>=$finishline) 
 {
  header("Location: copiedpasswd");
 }//end if
else 
 {
  $first += $interval;
  $last += $interval;
  header("Location: thenameofthisscript.php?first=$first&last=$last");
 }//end else

?>

Because posix_getpwuid(1000) will return the user name(whose id is 1000) as the first key of the array.

If You are useing kernel security module, such as LIDS, GrSec or Selinux it will work only if '/etc/passwd' is readable for user, under which PHP/Apache runs, otherwice you get FALSE.

To get the name of the owner of a file you can use something like this:

<?php
$startscript="/var/log/hello.log";

$fileowneruid=fileowner($startscript);
$fileownerarray=posix_getpwuid($fileowneruid);
$fileowner=$fileownerarray['name'];

echo "Owner is $fileowner";
?>

(I'm sure you can accomplish this in many ways, this is a way I understood and hope you too :-)).

Rolf

Here's a fairly safe way to get the username from uid even if the posix extension isn't installed.

<?php
function GetUsernameFromUid($uid)
{
  if (function_exists('posix_getpwuid'))
  {
    $a = posix_getpwuid($uid);
    return $a['name'];
  }
  # This works on BSD but not with GNU
  elseif (strstr(php_uname('s'), 'BSD'))
  {
    exec('id -u ' . (int) $uid, $o, $r);

    if ($r == 0)
      return trim($o['0']);
    else
      return $uid;
  }
  elseif (is_readable('/etc/passwd'))
  {
    exec(sprintf('grep :%s: /etc/passwd | cut -d: -f1', (int) $uid), $o, $r);
    if ($r == 0)
      return trim($o['0']);
    else
      return $uid;
  }
  else
    return $uid;
}
?>