1. The actual reason why the output file test.txt is empty is because the URL contains some special symbols, such as "&", which breaks the issued command. This can be fixed with proper quoting:

Code:

$output = shell_exec("echo '$uri' > /tmp/test.txt");

2. The syntax looks good, apart from the mentioned quoting. The interpretor/hashbang/shebang is not needed. It's outside the php section and is treated as plain text, so you can remove it. Inside the php section it would be a comment.

3. You write you get a blank page, but what did you expect? Due to echo'ing a string and redirecting it to a file there is no output to be returned. Add this to your php script to see some output:

Code:

$output2 = shell_exec('ls -l /tmp/test.txt');
echo "<pre>$output2</pre>";

4. Breaking down the URL is not a good idea. Try to figure out why.

Complete demo incl. shell script for processing the form data:

html file: unchanged

php file (script.php):
shell script (process-fields.sh):

Code:

#!/bin/bash
echo "BASH FIELD 1:    $1"
echo "BASH FIELD 2:    $2"
echo "BASH FIELD 3:    $3"

output:

Code:

08/25/2014 08/28/2014 info@example.com

BASH FIELD 1:    08/25/2014
BASH FIELD 2:    08/28/2014
BASH FIELD 3:    info@example.com

All in all it's nice to play with and stuff, but from the security point of view it's a big disaster, imho.
Learn the difference between GET and POST method, implement some form validation etc etc