is_dir() fails while scanning a directory in php

I'm trying to build a <ul> list with a <li> for each directory in a main folder. here's my code :

<?php

$dir = opendir(getEnv("DOCUMENT_ROOT") . "/folder");

while(($file = readdir($dir)) !== false ){
  if( is_dir($file) && $file !== "." && $file !== ".." ){
    echo "<li>" . $file . "</li>";
  }
}

closedir($dir);

?>

there are two directories in /home/example/folder but there are not recognized as folders (for sure they ar开发者_如何学JAVAe !)

if I "echo" the files in the while loop they are printed (they well exist for the script no trouble on that side). If I try to "filetype" them, a lstat failed error is thrown, I searched on internet the meaning of it and I end up with nothing but technically support that I pain to understand.

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Your problem is that inside "folder" directory you can have two directories (a and b),then the reading retrieve "a" and "b" as file names, while is_dir receive a full path filename or a relative filename, you have two options:

1. pass the full path to filename to the is_dir function (see example code).
2. pass the relative path (depends on where you put your script).

if( is_dir($dir . "/" . $file) && $file !== "." && $file !== ".." ){ ......

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Try:

while($file = readdir($dir)) {
   if (...) { }
}

The !== false portion is not required. if readdir reaches the end, it returns a false, and the loop will automatically terminate. Your version is being parsed as:

$file gets the value of (readdir($file) is not false)

e.g. you're assigning the boolean result of readdir($file) !== false, not the return value from readdir.

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to expand on my comment below, regarding operator precedence:

PHP's parse tree of your loop setup looks like this, expanded:

$bool = (readdir($dir) !== false);
$file = $bool;

To fix this, either remove the !== false portion entirely, or enforce your own precedence with extra brackets:

($file = readdir($dir)) !== false