Shell Scripts

A shell script is a file containing a series of commands and could be executed. It is commonly used to set up environment, run a program, etc.

You already know how to build a roslaunch file. It is very convenient to launch multiple ROS nodes and set parameters from a single roslaunch command. However, when developing robotic software with different packages, it might get harder to track errors and bugs generated from different nodes.

That's when shell scripts come in handy! After you create a shell script file to launch one or many nodes each in separate terminals, you will have the power to track the output of different nodes and keep the convenience of running a single command to launch all nodes.

Your launch.sh Script

Let us start by creating this launch.sh script in the Udacity Workspace. Its goal is to launch Gazebo and Rviz in separate instances of terminals. Note that we are using xterm terminal in the script here.

#!/bin/sh
xterm  -e  " gazebo " &
sleep 5
xterm  -e  " source /opt/ros/kinetic/setup.bash; roscore" & 
sleep 5
xterm  -e  " rosrun rviz rviz" 

The launch.sh shell script launches three terminals and issues one or multiple commands in each terminal. Let’s break down this script to understand the meaning of each line.

Code Breakdown

#!/bin/sh

This statement is called a shebang . It must be included in every shell script you write since it specifies the full path of the UNIX interpreter to execute it.

xterm -e " gazebo " &

With the xterm -e statement, we launch a new instance of an xterminal . Inside this terminal, we launch gazebo using the command "gazebo" . Then we add an ampersand & to indicate that another instance of an xterm terminal will be created in a separate statement.

sleep 5

We pause this script for 5 seconds using sleep .

xterm -e " source /opt/ros/kinetic/setup.bash; roscore" &

We launch a second instance of the xterm terminal. Inside this terminal, we source the ROS workspace and launch the ROS master node.

sleep 5

We pause this script for another 5 seconds.

xterm -e " rosrun rviz rviz"

We are launching a third instance of the xterm terminal, and running rviz.

Save your script file and give it execute pemission by chmod +x launch.sh . Then launch the shell script with ./launch.sh .

After launching this script, we’ll have three open xterm terminals, and we will be able to track any errors or bugs that occur. To recap, this script will open the first terminal and launch gazebo. Then it will pause for 5 seconds and open a second terminal to launch the ROS master. It will pause for another 5 seconds and, finally, open a third terminal to launch RVIZ.

Try to launch your script in the Workspace and verify its functions!

Task List:

Install xterm with sudo apt-get install xterm

Create a launch.sh file

Write one or multiple commands to be executed by the terminals

Turn your script into an executable one with chmod +x launch.sh

Launch the shell script file with ./launch.sh