launch XML <arg> 官方文档 翻译

<arg> tag

目录

1. <arg> tag
2. Introduction
3. Usecase pattern
4. Attributes
5. Examples
   1. Passing an argument to an included file
   2. Passing an argument via the command-line

Introduction

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>标记允许您创建更多可重用和可配置的启动文件（通过命令行传递的值，通过<include>传递的值）。或为更高级别的文件声明的值。 Args不是全局的。 arg声明特定于单个启动文件，非常类似于方法中的局部参数。 您必须像在方法调用中一样，将arg值显式传递给包含的文件。

 

Usecase pattern

<arg> can be used in one of three ways:

<arg>可以按三按方式使用

• <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).

  • 声明foo，foo必须作为命令行参数（如果是顶级）或通过<include>传递（如果包括）来传递。

  <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).

  • 使用默认值声明foo。 foo可以通过命令行参数（如果是顶级）或通过<include>传递（如果包括）来覆盖。

  <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.

  • 用常量值声明foo。 foo的值不能被覆盖。 这种用法使启动文件可以进行内部参数化，而无需在更高级别上暴露该参数化。

Attributes

• name="arg_name"

  • Name of argument.
  • 参数名

  default="default value" (optional)

  • Default value of argument. Cannot be combined with value attribute.

  • 参数的默认值。 不能与value属性结合使用。

  value="value" (optional)

  • Argument value. Cannot be combined with default attribute.

  • 参数值。 不能与默认属性结合使用。

  doc="description for this arg" (optional) New in Indigo

  • Description of the argument.
  • 参数声明

 

Examples

Passing an argument to an included file

向包含的文件传递参数

• my_file.launch:

  <include file="included.launch">
    <!-- all vars that included.launch requires must be set -->
    <arg name="hoge" value="fuga" />
  </include>

  included.launch:

  <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

通过命令行传递参数

roslaunch uses the same syntax as ROS remapping arguments to specify arg values.

roslaunch使用与ROS重映射参数相同的语法来指定arg值。

• $ 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