Warning
You're reading the documentation for a version of ROS 2 that has reached its EOL (end-of-life), and is no longer officially supported.
If you want up-to-date information, please have a look at Jazzy.
Migrating launch files from ROS 1 to ROS 2
This tutorial describes how to write XML launch files for an easy migration from ROS 1.
Background
A description of the ROS 2 launch system and its Python API can be found in Launch System tutorial.
Replacing an include tag
To have exactly the same behavior as Available in ROS 1, include
tags must be nested in a group
tag.
<group>
<include file="another_launch_file"/>
</group>
To replace the ns
attribute, push-ros-namespace
action must be used:
<group>
<push-ros-namespace namespace="my_ns"/>
<include file="another_launch_file"/>
</group>
Substitutions
Documentation about ROS 1’s substitutions can be found in roslaunch XML wiki.
Substitutions syntax hasn’t changed, i.e. it still follows the $(substitution-name arg1 arg2 ...)
pattern.
There are, however, some changes w.r.t. ROS 1:
env
andoptenv
tags have been replaced by theenv
tag.$(env <NAME>)
will fail if the environment variable doesn’t exist.$(env <NAME> '')
does the same as ROS 1’s$(optenv <NAME>)
.$(env <NAME> <DEFAULT>)
does the same as ROS 1’s$(env <NAME> <DEFAULT>)
or$(optenv <NAME> <DEFAULT>)
.find
has been replaced withfind-pkg-share
(substituting the share directory of an installed package). Alternativelyfind-pkg-prefix
will return the root of an installed package.There is a new
exec-in-pkg
substitution. e.g.:$(exec-in-pkg <package_name> <exec_name>)
.There is a new
find-exec
substitution.arg
has been replaced withvar
. It looks at configurations defined either witharg
orlet
tag.eval
anddirname
substitutions haven’t changed.anon
substitution is not supported.
Type inference rules
The rules that were shown in Type inference rules
subsection of param
tag applies to any attribute.
For example:
<!--Setting a string value to an attribute expecting an int will raise an error.-->
<tag1 attr-expecting-an-int="'1'"/>
<!--Correct version.-->
<tag1 attr-expecting-an-int="1"/>
<!--Setting an integer in an attribute expecting a string will raise an error.-->
<tag2 attr-expecting-a-str="1"/>
<!--Correct version.-->
<tag2 attr-expecting-a-str="'1'"/>
<!--Setting a list of strings in an attribute expecting a string will raise an error.-->
<tag3 attr-expecting-a-str="asd, bsd" str-attr-sep=", "/>
<!--Correct version.-->
<tag3 attr-expecting-a-str="don't use a separator"/>
Some attributes accept more than a single type, for example value
attribute of param
tag.
It’s usual that parameters that are of type int
(or float
) also accept an str
, that will be later substituted and tried to convert to an int
(or float
) by the action.