Why can I not find the file if I give the relative path but I can find it with the direct path?

Question

I'm trying to use mime->addAttachment() to add an attachmen to an email i'm about to send

relative path: ../../clientdata/client1/attachments/file.txt

direct path: /home/hosting/site.eu/html/ssl/clientdata/client1/attachments/file.txt

script location: /home/hosting/site.eu/html/ssl/work/php_scripts/send_email.php

send_email.php is executed using:

exec("php /home/hosting/site.eu/html/ssl/work/php_scripts/send_email.php");

Is there something I'm missing here?

The code i'm using to add the attachment:

$f = 'ssl.site.eu/clientdata/client1/attachments/file1.txt';  
$arr_file = explode('/', $f, 2);
$file_path = '/home/hosting/site.eu/html/ssl/'.$arr_file[1]; //this works
// $file_path = '../../'.$arr_file[1]; // this doesn't work;
$mime->addAttachment($file_path,'application/octet-stream');

Answer 1

Beware the working directory of your process.

Now does the following code give the currect path? echo getcwd().$relative_path;

PHP getcwd()

Answer 2

if you include some PHP files that relative the file that codes execute,you must be sure that you include these files relative the process's current directory,but not the file contains current executing codes.