gistfile1.php

<?php
$var          =    NULL    ""        0     "0"        1

strlen($var)  =    0       0         1      1         1
is_null($var) =    TRUE    FALSE   FALSE    FALSE    FALSE
$var == ""    =    TRUE    TRUE    TRUE     FALSE    FALSE
!$var         =    TRUE    TRUE    TRUE     TRUE     FALSE
!is_null($var)=    FALSE   TRUE    TRUE     TRUE     TRUE
$var != ""    =    FALSE   FALSE   FALSE    TRUE     TRUE
$var          =    FALSE   FALSE   FALSE    FALSE    TRUE