I found on the web a snippet of PHP code that supposedly does what I need: encrypt a small file received through a CGI routine, however I cannot get it to work probably due to my very basic knowledge of PHP, here is the code:

enc.php
<?php
$gpg='/usr/bin/gpg';
$nam='myname@internode.on.net';
$ifile='file2encode.txt';
echo shell_exec("$gpg -e -r $nam $ifile");
?>

Typing "http://192.168.1.13/cgi-bin/enc.php in the browser gives
"exec format error on enc.php"
in /var/log/httpd/error_log

The following code entered at the command line works:
$ gpg -e -r myname@internode.on.net file2encode.txt

Can you help with this?

Thank you.

well i'm not sure what the problem is

i tried your code using commandline php and it worked
so try this one

<?php
$gpg='/usr/bin/gpg';
$nam='myname@internode.on.net';
$ifile='file2encode.txt';
$retval=`$gpg -e -r $nam $ifile`;
echo $retval;
?>

or

<?php
$gpg='/usr/bin/gpg';
$nam='myname@internode.on.net';
$ifile='file2encode.txt';
system("$gpg -e -r $nam $ifile",$retval);
echo $retval;
?>

but i think both won't work
because i think you have a failure configuration of the apache
do you have php configured?
i think apache (or whatever you use for http server) just does not know what to do with a php file

I have Apache (httpd) configured and working. I have a number of CGI routines in /var/www/cgi-bin that Apache has no problem to find and execute (I just checked it)

But if the script works on your machine, the bug is not in the script.
You were right, your suggestions didn't work.

Thank you for the hint.
I misread your question: no I didn't configure PHP.

Checking this directory (/var/www/cgi-bin), I found there is no PHP script in it, could it have something to do with PHP?

ok, let's figure it out ;-)

1. google told me that "exec format error on ..." most time means, that the program can't be executed
think about just copy a .exe from windows to a linux distri, make a chmod, and try to execute the .exe file
i didn't try it, but you should get something like "exec format error on" because linux (the operating system itself) doesn't understand the .exe format

http://minitutorials.com/apache/php12.shtml
http://www.thesitewizard.com/archive/php4install.shtml (for windows, but interesting too)
http://www.webmasterstop.com/48-3.html (windows too)
http://docs.php.net/en/install.unix.apache.html

2. you said you have many cgi routines in /var/www/cgi-bin but no PHP script!
i wrote a cgi prog in C for windows and linux and as far as i know a CGI program is nothing else than a simple executable file which uses environment variables and printf to get apache information and print the response which is shown to the user

i'm not sure, but i never had a php script in cgi-bin!
because a php script is something different! you need php to interpret the script

i'm thinking about 2 problems:
1. i think php itself isn't correctly configured in your apache or the php script itself has to be in a different directory than cgi-bin
(check, apache php configuration and read through some php apache manuals)
2. i don't know if it will work, but heres a workaround
change the script to:

#!/usr/bin/php
<?php
$gpg='/usr/bin/gpg';
$nam='myname@internode.on.net';
$ifile='file2encode.txt';
echo shell_exec("$gpg -e -r $nam $ifile");
?>


the only difference is the first line (#!/usr/bin/php)
you have to change #!/usr/bin/php to the right path to the php executable! (but in most cases it should work)
then make chmod for your script (the script is in cgi-bin already!!) to make it executable

in the command line try
/var/www/cgi-bin/enc.php

if this works!
you can try to use it in the browser (just like you did already)

it's just a workaround

We're progressing!
I changed the line as you suggested: #!/usr/bin/php
Accessing enc.php from the command line gives:
usage: gpg [options] --encrypt [filename]
Content-type: text/html
X-Powered-By: PHP/4.3.4

And accessing through the browser gives:
Security Alert! The PHP CGI cannot be accessed directly.
This PHP CGI binary was compiled with force-cgi-redirect enabled. This means that a page will only be served up if the REDIRECT_STATUS CGI variable is set, e.g. via an Apache Action directive.
For more information as to why this behaviour exists, see the manual page for CGI security.
For more information about changing this behaviour or re-enabling this webserver, consult the installation file that came with this distribution, or visit the manual page.

I'll have a good look at the manuals but I think I'll probably need to open a thread about HTTPD config.