Question

I need to execute kdiff3 command in my desktop machine (localhost) from PHP script (using browser, not command line). I’ve given permission for the user www-data that is executing the scripts to execute kdiff3 using visudo. In fact, if I log in as www-data I can execute it without problems (sudo kdiff3 …, it’s configured to not ask for a password at all).

The problem is when I try to execute this command from a PHP script. I’ve tried this:

$output = shell_exec("sudo kdiff3 -m $file.def.old $file $file.def -o $file");

and nothing happens (output is NULL). If I try a non interactive command, like ls it works:

$output = shell_exec("ls");

What’s happening? Why cannot execute an interactive command?

Answer 1

kdiff3 is an interactive graphical user interface program, so it use KDE and Qt and requires an X11 server.

And within a web server (i.e. in PHP running for Apache or Lighttpd) you don’t have any X11 server.

So there is no way to use kdiff3 from inside a PHP script (unless the web server is running on your desktop Linux machine; and then you need to set appropriately the environment, notably DISPLAY and probably XAUTHORITY environment variable). However you could run a command line program like diff3 … (using the popen tricks).