Hi Brian,

The $( ) form seems to be just as valid as backticks for command 
substitution in bash. See the comments just before example 12-3 on this 
page:

http://tldp.org/LDP/abs/html/commandsub.html

Sorry for turning this thread into a bash discussion :)

Joel

Brian Gerkey wrote, On 22/07/10 18:12:
> On Thu, Jul 22, 2010 at 2:57 AM, Joel Cartwright
> <J.J.Cartwright@hw.ac.uk>  wrote:
>> Perhaps it would be simpler to use the $( ) alternative to ` `, where
>> there is less possibility for confusion over characters. As below:
>>
>>         rosrun rviz rviz -d $(rospack find turtle_tf) /rviz/turtle_rviz.vcg
>
> hi Joel,
>
> The backtick characters are part of bash syntax.  We can't do much about that.
>
> 	brian.
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-- 
Research Associate
Ocean Systems Laboratory
Heriot-Watt University, UK