New in C Turtle
The <arg> tag allows you to create more re-usable and configurable launch files by specifying values that are passed via the command-line, passing in via an <include>, or declared for higher-level files. Args are not global. An arg declaration is specific to a single launch file, much like a local parameter in a method. You must explicitly pass arg values to an included file, much like you would in a method call.
<arg> can be used in one of three ways:
<arg name="foo" />
Declares the existence of foo. foo must be passed in either as a command-line argument (if top-level) or via <include> passing (if included).
<arg name="foo" default="1" />
Declares foo with a default value. foo can be overriden by command-line argument (if top-level) or via <include> passing (if included).
<arg name="foo" value="bar" />
Declares foo with constant value. The value for foo cannot be overridden. This usage enables internal parameterization of a launch file without exposing that parameterization at higher levels.
- Name of argument.
default="default value" (optional)
Default value of argument. Cannot be combined with value attribute.
Argument value. Cannot be combined with default attribute.
doc="description for this arg" (optional) New in Indigo
Description of the argument. You could get this through --ros-args argument to the roslaunch command.
Passing an argument to an included file
<include file="included.launch"> <!-- all vars that included.launch requires must be set --> <arg name="hoge" value="fuga" /> </include>
<launch> <!-- declare arg to be passed in --> <arg name="hoge" /> <!-- read value of arg --> <param name="param" value="$(arg hoge)"/> </launch>
Passing an argument via the command-line
roslaunch uses the same syntax as ROS remapping arguments to specify arg values.
$ roslaunch my_file.launch hoge:=my_value (.launch file is available at the current dir) $ roslaunch %YOUR_ROS_PKG% my_file.launch hoge:=my_value