using popen on unix

[Anon]

Hi there I could use some help understanding why I am not able to process
this Unix command properly in my php code.
From the bash this is what it looks like...

cat /opt2/home3/blah/public_html/temp/header.txt|/usr/lib/sendmail [e-mail]

the script was set up to process a temp file I set up, one that contains mail-header info
(temp file = header.txt) to provide a return path if messages get bounced-
I could not get this to work in the php mail() but does this function in fact have return-path capability?

Any ways, my code looks like this..
$remind_email = "dynamically assigned"

$fp = popen('cat /opt2/home3/blah/public_html/temp/header.txt|/usr/lib/sendmail ' . $remind_email,'r');

Does php send along characters such as the . and , what is happening here?

Thanks in advance,
C

[Anon]

I just notice I forgot the ; in the variable
assignment but this is not the case in my code.

C