Add "output" option to launch

[Tiryoh]

This PR adds and "output" option to timed_roslaunch.launch.

[achille-martin]

This PR is nice and useful.

However, there seems to be a way to add "output" arg when passing arguments to the next launch file: http://wiki.ros.org/timed_roslaunch

Instead of using the format <include file="$(find timed_roslaunch)/launch/timed_roslaunch.launch"></include>
It is recommended to use the format <node pkg="timed_roslaunch" type="timed_roslaunch.sh" args="" name="timed_roslaunch" output="screen" />

The outcome is the same, except that this time, output can be specified.

This is probably why the PR has not been merged yet.
Although it would be consistent to add "output" arg availability to the first format (the <include> one).

[Tiryoh]

Hi @achille-martin, thanks for your comment.

I agree with you that almost the same functionality as this PR has already been implemented.
However, this PR adds changes that make it more convenient when we use timed_roslaunch with output="screen" option.

For example, in order to rewrite only a specific argument using if/unless, we can implemented as follows.

<launch>
  <node pkg="timed_roslaunch" type="timed_roslaunch.sh" args="2 turtlebot_navigation amcl_demo.launch initial_pose_x:=0.0 initial_pose_y:=0.0" name="timed_roslaunch" output="screen" if="$(arg foo)" />
  <node pkg="timed_roslaunch" type="timed_roslaunch.sh" args="2 turtlebot_navigation amcl_demo.launch initial_pose_x:=17.0 initial_pose_y:=17.0" name="timed_roslaunch" output="screen" unless="$(arg foo)" />
</launch>

If we apply this PR, we will be able to implement it more simply.

<launch>
  <include file="$(find timed_roslaunch)/launch/timed_roslaunch.launch">
    <arg name="time" value="2" />
    <arg name="pkg" value="turtlebot_navigation" />
    <arg name="file" value="amcl_demo.launch" />
    <arg name="value" value="initial_pose_x:=0.0 initial_pose_y:=0.0" if="$(arg foo)" />
    <arg name="value" value="initial_pose_x:=17.0 initial_pose_y:=17.0" unless="$(arg foo)" />
    <arg name="node_name" value="timed_roslaunch" />
    <arg name="output" value="true" />
  </include>
</launch>

[achille-martin]

Hi @Tiryoh,

Thanks for the details on specific use cases, I would agree with you on the feature.