[apache@h185 default]$ ls -l /home/www/default/p.php
-rwxr-xr-x. 1 zhouhh zhouhh 50837 Aug 28 19:02 /home/www/default/p.php
[apache@h185 default]$ ls -l /usr/bin/rrdtool
-rwxr-xr-x. 1 root root 24688 Aug 21  2010 /usr/bin/rrdtool
[apache@h185 default]$ ls -l /root/my.cnf
ls: cannot access /root/my.cnf: Permission denied
[apache@h185 default]$ ls -l /usr/bin/ld
-rwxr-xr-x. 1 root root 594968 Jun 22 22:06 /usr/bin/ld
[apache@h185 default]$ ls -l /usr/bin/php
-rwxr-xr-x. 1 root root 3224944 Jul  4 00:57 /usr/bin/php
[apache@h185 default]$ vi test.php
[apache@h185 default]$ cat test.php
<?php
#if(is_file('/home/www/default/p.php'))

#if(is_file('/usr/bin/rrdtool'))
#if(is_file('/root/my.cnf'))
#if(is_file('/usr/bin/ld'))
#if(file_exists('/usr/bin/ld'))
if(is_file('/usr/bin/php'))
{
print 'ok';
}
else
{
print 'no ok';
}
?>
[apache@h185 default]$

if(!is_dir($filename)) {
  //remove a file
  unlink($filename);
} else {
  //remove a directory
}