line 1: using exec() to produce a directory listing...
line 7: exec('ls -al .', $output, $return );...
line 21: the next 9 characters are 3 groups of 3 characters each, which tell the read/write/execute permissions for user, group, and other respectively:...
line 24: x = execute...
line 25: using the above example of lrwxr-xr-x, you would have symbolic link file, where the user can read, write and execute (rwx), and the group and others can read and execute (r-x)...

line 1: This checks the name of the PHP file currently executing....
line 3: because you didn't intend for anyone to execute this file on its own....
line 6: and the program will continue to execute....

line 44: //execute query...
line 46: or die("Couldn't execute query:<br>" . mysql_error(). "<br>" . mysql_errno());...