On Fri, Apr 16, 2010 at 8:50 AM, Blaise Gassend <blaise@willowgarage.com>wrote:

> I have asked Ken why there is no $(command ) macro in roslaunch but
> never got an answer... I have seen cases beyond parameters where it
> would have been handy... but perhaps hacky.
>
>
Must have slipped my mind because I don't recall a ticket. My only issues
with command hacks is that it is much easier to put something in there that
is non-portable, and validation is much, much trickier. It has its uses,
though.

I've always wanted to a top-level <exec> or <command> tag to complement the
<node> tag as many things that are called <node>s in roslaunch are not
actually ROS nodes (and can have different assumed behaviors). We attempted
to design this prior to ROS 1.0, but it quickly spiraled out of control with
respect to scope. Unlike nodes, commands are sequence-able because they
normally terminate, unlike nodes which do not. Once you attempt to add
sequencing to roslaunch for a particular tag, things the design space gets
arbitrarily large (especially when considering remote launches).

I was hoping to have more time to overhaul the roslaunch syntax this
iteration, but it looks like that won't happen until D-Turtle.

 - Ken