Running a planner executable from a node

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Hello,

I have created a service call that runs a terminal command which is running an executable. I am integrating the PDDL into ROS(kinetic). To run the command simply on terminal I type :

./ff -p /home/mydirectory/pddl_files/ -o domain.pddl -f problem.pddl > solution.txt

As a python file I am able to run it like this:

import os
os.system("./ff -p /home/mydirectory/pddl_files/ -o domain.pddl -f problem.pddl > solution.txt")

It runs fine in terminal and as a python file but in ROS it gives me the following error:

sh: 1: ./ff: not found