[ROS Q&A] 147 – How to make a Python file executable?

One of the most frequent question that we get in our customer support channels is an error when trying to ‘rosrun’ a Python file. The package is there, the file is there, the command has been typed in correctly, but it doesn’t want to run. Sounds familiar?

This is usually due to the file’s permission, which had to be set to be executable. So in this video, we will see how to do this, as well as explore a bit more on this subject. Beginners of ROS and the Linux system should find this very useful.

RELATED LINKS

▸ Original question
▸ ROS Development Studio (ROSDS)
▸ Robot Ignite Academy

Step1. Create a project in Robot Ignite Academy(RIA)

We have the best online ROS course available in RIA. It helps you learn ROS in the easiest way without setting up ROS environment locally. The only thing you need is a browser! Create an account here and start to browse the trial course for free now! We’ll use the ROS Basics in 5 Days course unit 2 as an example today.

Step2. How to make .py file executable

Here we create a package called test_exec using the following command

cd catkin_ws/src
catkin_create_pkg test_exec rospy

We create a file called simple_topic_publisher.py under the src folder and copy the code from the course.

Then we compile the package using

cd ~/catkin_ws
catkin_make

Now we try to run the .py file with rosrun test_exec simple_topic_publisher.py  , but got the same error as the question.

How to solve this problem? We can execute the following command to give the file execute permission

chmod +x simple_topic_publisher.py

You can also check if the file has the permission with

ls -l

Then we run the file again with the rosrun command, the file is able to execute now.

Want to learn more?

If you are interested in learning ROS, please check our Robot Ignite Academy.

Edit by: Tony Huang

Feedback

Did you like this video? Do you have questions about what is explained? Whatever the case, please leave a comment on the comments section below, so we can interact and learn from each other.

If you want to learn about other ROS topics, please let us know on the comments area and we will do a video about it.

[ROS Q&A] 146 – Command line argument passing in rosrun

In this video we are going to explore how to pass an argument through command line using rosrun.

It can be a bit confusing, but we are going to explain the difference of the return of the method depending of the type of the value you pass to the argument.

Step 1. Create a project in ROS Development Studio(ROSDS)

ROSDS helps you follow our tutorial in a fast pace without dealing without setting up an environment locally. If you haven’t had an account yet, you can create a free account here. Let’s call the project rosrun_param.

Step 2. Create package

We’ll create a package for our code with the roscpp and std_msgs dependency.

cd ~/catkin_ws/src
catkin_create_pkg my_pkg roscpp std_msgs

Under the my_pkg/src folder, create a my_pkg_node.cpp file with the code from the question.

#include <ros/ros.h>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{  
  std::string param;
  ros::init(argc, argv, "node_name");
  ros::NodeHandle nh("~");
  ROS_INFO("Got parameter : %s", param.c_str());

  if(nh.getParam("blue", param))
  {
    cout << "blue" << endl;
  }
  else if(nh.getParam("green", param))
  {
    cout<< "green" << endl;
  }        
  else
  {
    cout << "Don't run anything !! " << endl;
  }
  return 0;
}

To compile the code, we have to modify the CMakeLists.txt file. Please uncomment the add_executable and target_link_libraries in the build part.

Then we can compile the code with

cd ~/catkin_ws
catkin_make

After compile, we can run the executable with

rosrun my_pkg my_pkg_node

The output is just don’t run anything because we didn’t pass any argument yet.

As an example, we can pass arguments like the following

rosrun my_pkg my_pkg_node _blue:=text

Then the output is blue.

However, the code doesn’t quite make sense. Let’s modify it.

#include <ros/ros.h>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{  
  std::string param;
  ros::init(argc, argv, "node_name");
  ros::NodeHandle nh("~");
  nh.getParam("param", param)
  ROS_INFO("Got parameter : %s", param.c_str());

  if(param.compare("blue")==0)
  {
    cout << "blue" << endl;
  }
  else if(param.compare("green")==0)
  {
    cout<< "green" << endl;
  }        
  else
  {
    cout << "Don't run anything !! " << endl;
  }
  return 0;
}

Now if you pass blue or green as arguments, it will print the color. If you pass something else, it will run nothing.

Want to learn more?

If you are interested in ROS and want to learn more about it, please check our ROS Basics C++ Course.

Edit by: Tony Huang

RELATED LINKS

▸ ROS Development Studio (RDS)
▸ Robot Ignite Academy
▸ ROS Basics C++ Course

Feedback

Did you like this video? Do you have questions about what is explained? Whatever the case, please leave a comment on the comments section below, so we can interact and learn from each other.

If you want to learn about other ROS topics, please let us know on the comments area and we will do a video about it.