filesystem.md

The ROS Filesystem

Now that you have gotten a little experience with ROS you're ready to start working within the ROS file system.

Quick Overview of Filesystem Concepts

Packages

Packages are the software organization unit of ROS code. Each package can contain libraries, executables, scripts, or other artifacts. The turtlesim_node and turtle_teleop_key nodes which you started previously are both contained within the turtlesim package. The rqt_graph node is contained inside the rqt_graph package.

Manifest

A manifest is a description of a ''package''. Its serves to define dependencies between packages and to capture meta information about the package like version, maintainer, license, etc...

Filesystem Tools

Code is spread across many ROS packages. Navigating with command-line tools such as ls and cd can be very tedious which is why ROS provides tools to help you.

rospack

rospack allows you to get information about packages. In this tutorial, we are only going to cover the find option, which returns the path to package. Usage:

rospack find [package_name]

Example:

rospack find roscpp

Would return:

 YOUR_INSTALL_PATH/share/roscpp

If you installed ROS kinetic with apt on Ubuntu Linux you would see exactly: /opt/ros/kinetic/share/roscpp

roscd

roscd is part of the rosbash suite. It allows you to change directory cd directly to a package or a stack. Usage:

 roscd [locationname[/subdir]]

Run this example:

 roscd roscpp

To verify that we have changed to the roscpp package directory. Now let's print the working directory using the Unix command pwd:

You should see:

 YOUR_INSTALL_PATH/share/roscpp

You can see that YOUR_INSTALL_PATH/share/roscpp is the same path that rospack find gave in the previous example. Note that roscd, like other ROS tools, will only find ROS packages that are within the directories listed in your ROS_PACKAGE_PATH.

To see what is in your ROS_PACKAGE_PATH

 echo $ROS_PACKAGE_PATH

Your ROS_PACKAGE_PATH should contain a list of directories where you have ROS packages separated by colons. Here is a typical example

 /opt/ros/kinetic/base/install/share:/opt/ros/kinetic/base/install/stacks

roscd can also move to a subdirectory of a package or stack. Try:

 roscd roscpp/cmake
 pwd

You should see:

 YOUR_INSTALL_PATH/share/roscpp/cmake

roscd log

roscd log will take you to the folder where ROS stores log files. Note that if you have not run any ROS programs yet, this will yield an error saying that it does not yet exist. If you have run some ROS program before, try: roscd log

rosls

rosls is also part of the rosbash suite. It allows you to ls directly in a package by name rather than by absolute path. Usage:

 rosls [locationname[/subdir]]

Example:

 rosls roscpp_tutorials

Would return:

 cmake launch package.xml  srv

Tab Completion

It can get tedious to type out an entire package name. In the previous example, roscpp_tutorials is a fairly long name. Luckily, some ROS tools support TAB completion. Start by typing:

 roscd roscpp_tut<<< now push the TAB key >>>

After pushing the TAB key, the command line should fill out the rest: roscd roscpp_tutorials/ This works because roscpp_tutorials is currently the only ROS package that starts with roscpp_tut. Now try typing:

 roscd tur<<< now push the TAB key >>>

After pushing the TAB key, the command line should fill out as much as possible: roscd turtle However, in this case there are multiple packages that begin with turtle. Try typing TAB another time. This should display all the ROS packages that begin with turtle:

 turtle_actionlib/  turtlesim/  turtle_tf/

On the command line you should still have:

 $ roscd turtle

Now type a s after turtle and then push TAB:

 roscd turtles<<< now push the TAB key >>>

Since there is only one package that start with turtles, you should see:

 roscd turtlesim/

Review

You may have noticed a pattern with the naming of the ROS tools:

• rospack = ros + pack(age)
• roscd = ros + cd
• rosls = ros + ls

This naming pattern holds for many of the ROS tools.