When posix_getgrgid() fails (e.g. an invalid/unknown group id), it returns false.
This is except for Mac OSX on which you get an array with name "nogroup" and gid of "-1".
    (PHP 4, PHP 5, PHP 7, PHP 8)
posix_getgrgid — Return info about a group by group id
$group_id
   ) : array|falseGets information about a group provided its id.
group_idThe group id.
The array elements returned are:
| Element | Description | 
|---|---|
| name | The name element contains the name of the group. This is a short, usually less than 16 character "handle" of the group, not the real, full name. | 
| passwd | The passwd element contains the group's password in an encrypted format. Often, for example on a system employing "shadow" passwords, an asterisk is returned instead. | 
| gid | Group ID, should be the same as the group_idparameter used when calling the
        function, and hence redundant. | 
| members | This consists of an array of string's for all the members in the group. | 
false on failure.
  
 
Example #1 Example use of posix_getgrgid()
<?php
$groupid   = posix_getegid();
$groupinfo = posix_getgrgid($groupid);
print_r($groupinfo);
?>
以上例程的输出类似于:
Array
(
    [name]    => toons
    [passwd]  => x
    [members] => Array
        (
            [0] => tom
            [1] => jerry
        )
    [gid]     => 42
)
When posix_getgrgid() fails (e.g. an invalid/unknown group id), it returns false.
This is except for Mac OSX on which you get an array with name "nogroup" and gid of "-1".
    
in php-4.3 the array returned seems to have changed.
it now returns:
["name"] group name
["passwd"] group password
["members"] group members (array of usernames)
["gid"] numeric group id
    
okies...
This code should be considered as an OPTION only, it works under MY set of circumstances, and that is all I intended. The below funtion will return the NAME of the GROUP if provided with the Group ID#
  function RC_posix_getgrgid($gid) 
    {
    $LocationGroup = "/etc/group"; //EDIT THIS IF YOU HAVE A DIFFERENT OS. mine = debian
    $fp = fopen ("/etc/group","r");
    while ($groupinfo = fscanf ($fp, "%[a-zA-Z0-9]:x:%[0-9]:%[a-zA-Z0-9]\n")) 
        {
        list ($name, $groupID, $nfi) = $groupinfo;
        if ($groupID == $gid)
            {
            $returnval = $name;
            }
        }
    fclose($fp);
    if($returnval) { return $returnval; } else { return 0; }
    }
    
Returns an array containing the elements of the group structure. The array has both numeric indices, each of which is a string naming one member of the group, and named string indices. The array elements are:
$_["name"]  string groupname (users)
$_["gid"] integer gidnumber (e.g. 0 for wheel/root)
$_["members"] int number of users in group
$_[0]..$_[n] string usernames in the group