Unable to call a python script through PHP - php

Question

I Have been stuck for a couple of days now. I am attempting to call a simple python script from PHP. For the life of me I cannot figure out what the issue is. I have made the onoff.py script executable with chmod +x.
I can run the script just fine from the command line like this:
pi#raspberrypi:/var/www/html $ python onoff.py
LED on
LED off
My issue is when I try to call the script from PHP. I get nothing.
My Python Script:
#!/usr/bin/python
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(18,GPIO.OUT)
print "LED on"
GPIO.output(18,GPIO.HIGH)
time.sleep(1)
print "LED off"
GPIO.output(18,GPIO.LOW)
My PHP Script:
<?php
$command = escapeshellcmd('python /var/www/html/onoff.py');
$output = shell_exec($command);
echo $output;
?>
Any help is greatly appreciated!
EDIT:
if I change my onoff.py script to a simple while loop such as:
#!/usr/bin/python
x=1
while (x<10):
print x
x=x+1
the output on the browser is:
1 2 3 4 5 6 7 8 9
I just don't understand why the loop will run but I get no output with the original python code.
EDIT 2:
Ok So I taking a different approach and trying to see where the code fails. I am adding bits of code at a time. Please see the following.
#!/usr/bin/python
import random
import time
import RPi.GPIO as GPIO
randomNumber = random.randint(1, 20)
GPIO.setmode(GPIO.BCM)
#GPIO.setup(18,GPIO.OUT)
print randomNumber
Now when I run the PHP it shows a random number so I know the python script is running. When I un-comment GPIO.setup(18,GPIO.OUT) and run the php I get a blank screen. I have no idea why this would make the script fail.

Answer 1

shell_exec() will only return a string if $command a). Ran OK and assuming b). that it spits its response to STDOUT.
Use exec() and pass it your command, an integer $code and an empty array $response both of which are treated by PHP as arguments by reference.
Run your command thus:
$command = escapeshellcmd('/path/to/python /var/www/html/onoff.py');
$response = array();
$code = 0;
exec($command, $response, $code);
var_dump($code, $response);
die;
You should now see what is actually being given to PHP internally and why the Python script isn't working.

Answer 2

You need to use python before the script, i.e.:
$command = escapeshellcmd('python /var/www/html/onoff.py');
If it doesn't work, python probably ins't on the PATH of the apache user and you may need to use the full path to the python binary, use which to find the full path:
which python
//usr/bin/python
The use that value:
$command = escapeshellcmd('/usr/bin/python /var/www/html/onoff.py');
Note:
Make sure apache user has execute permissions on onoff.py