Currently in launch an executed process does not have anything printed to the console and nothing is logged to a file.

Some of the examples will create custom event handlers for this:

The "default launch description" provided by launch_ros also creates an event handler to cause executed processes to print to the console if configured to do so (with the output= option to ExecuteProcess and it's derived classes like Node):

But even this doesn't handle writing process output to a log file:

Ideally, there would be some facility for this built into launch and launch_ros could additionally configure it to write files to something like ROS_HOME where as it might go to ~/.launch_logs (or something like that) instead. The user could further configure this default event handler if desired.

The user would still be able to provide their own event handler for output from process, to be run along with the default or instead of it.