Cannot set custom ROS_HOME in launch file

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Hi!

I want to have a current directory for my node different than ~/.ros, so that when I create files in my node providing only local file name, they are saved relevant to my given $ROS_HOME. I tried the following launch file:

<?xml version="1.0"?>
<launch>
   <env name="ROS_HOME" value="/home/alex" />
   <node name="test" type="test.py" pkg="simple_pcl" output="screen"/>
</launch>

But the file I am creating still appears in ~/.ros. Here is the node source:

#!/usr/bin/python

import os

if __name__ == '__main__':
    os.system('touch test_file')

I also tried setting ROS_HOME inside node entry:

<?xml version="1.0"?>
<launch>
  <node name="test" type="test.py" pkg="simple_pcl" output="screen">
    <env name="ROS_HOME" value="/home/alex" />
  </node>
</launch>

also without success. What do you think is the problem?