ros2+＜arg＞/＜env＞/＜set_env＞/＜env＞/＜param＞比较

<env>

• Available in ROS 1.

• Sets an environment variable.

• It has been replaced with?env,?set_env?and?unset_env:

  • env?can only be used nested in a?node?or?executable?tag.?if?and?unless?tags aren’t supported.

  • set_env?can be nested within the root tag?launch?or in?group?tags. It accepts the same attributes as?env, and also?if?and?unless?tags.

  • unset_env?unsets an environment variable. It accepts a?name?attribute and conditionals.

arg?

• Available in ROS 1.

• arg?is used for declaring a launch argument, or to pass an argument when using?include?tags.

• Differences from ROS 1:

  • value?attribute is not allowed. Use?let?tag for this.

  • doc?is now?description.

  • When nested within an?include?tag,?if,?unless, and?description?attributes aren’t allowed.

param?

• Available in ROS 1.

• Used for passing a parameter to a node.

• There’s no global parameter concept in ROS 2. For that reason, it can only be used nested in a?node?tag. Some attributes aren’t supported in ROS 2:?type,?textfile,?binfile,?executable.

• The?command?attribute is now?value="$(command?'...'?)".