php exec() and shell_exec()

Question

I currently have a php page that my webserver serves. In order to display all the information I need to display on the page I need output from an external python script. So I have been using the exec() command of php to execute the python script and capture the output in an array of strings as follows:

$somequery = $_GET['query'];
$result = exec("python /var/www/html/query/myscript.py ".somequery."");

//some for loop to loop through entries in result and echo them.

However there are never any entries to be printed, yet when I run the command directly on the console of the server it will output correctly. I've tried echoing out the command on the webpage that I am executing and it's the correct command. The only thing I think it can be is that exec() doesn't stop the rest of the php program from executing before it finishes, leading to the loop i have printing out entries finding that $result is empty.

How can I ensure that exec() finishes executing before the rest of my php script? Are there maybe settings in php.ini that I would need to change? I'm not entirely sure.

EDIT: I've tried running and storing the output of shell_exec("echo hello"); and printing that output, it now prints. However, when running my command that takes a few seconds longer, the program never finishes executing it before going to the next line.

EDIT 2: I found my solution in the following post https://stackoverflow.com/a/6769624 My issue was with with the numpy python package I was using and I simply needed to comment out the line in /usr/lib64/python2.7/ctypes/init.py like the poster did and my script output correctly.

FYI, that's completely insecure. Anyone can run anything that your web server user has access to. Be very careful with exec(). — Brad
– Brad, Commented Dec 16, 2012 at 1:10
It may have been asked, but none of those answers answer my question. I also am aware this insecure, this isn't for a production environment however.. just a proof of concept. — EthanLWillis
– EthanLWillis, Commented Dec 16, 2012 at 1:16
i think you need to use full path to python binary like /usr/bin/python — zb'
– zb', Commented Dec 16, 2012 at 1:32

ashiina · Accepted Answer · 2012-12-16 01:31:02Z

2

The correct way to get your shell output is like this:

exec("python /var/www/html/query/myscript.py ".somequery."", $result);

var_dump($result); //output should be in here

Give it a try.

answered Dec 16, 2012 at 1:31

ashiina

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2 Comments

ashiina Over a year ago

On a side note: putting the $_GET value directly into your exec() command without any sanitization is VERY dangerous. Easy example, if someone inserts $_GET['query'] as ` && rm -rf /` (DO NOT attempt to try this), you just got your whole server deleted. Be sure to run it through some kind of sanitization.

EthanLWillis Over a year ago

php.net/manual/en/function.escapeshellarg.php I use this when I'm actually running it on an accessible server. Also, I did a var_dump after running it your way and I simply get array(0) {}

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