如何在ros2熟悉和使用各種指令呢，ros1的經典小烏龜是最快捷的途徑之一。
ros2_tutorials(turtlesim): https://github.com/zhangrelay/ros2_tutorials
通過turtlesim，對比一下ros1和ros2吧：
檔案組織：
ros1：
.
├── CHANGELOG.rst
├── CMakeLists.txt
├── images
│ ├── box-turtle.png
│ ├── diamondback.png
│ ├── electric.png
│ ├── fuerte.png
│ ├── groovy.png
│ ├── hydro.png
│ ├── hydro.svg
│ ├── indigo.png
│ ├── indigo.svg
│ ├── jade.png
│ ├── kinetic.png
│ ├── kinetic.svg
│ ├── lunar.png
│ ├── lunar.svg
│ ├── melodic.png
│ ├── palette.png
│ ├── robot-face.png
│ ├── robot-turtle.png
│ ├── sea-turtle.png
│ ├── turtle.png
│ └── turtle.xar
├── include
│ └── turtlesim
│ ├── turtle_frame.h
│ └── turtle.h
├── launch
│ └── multisim.launch
├── msg
│ ├── Color.msg
│ └── Pose.msg
├── package.xml
├── src
│ ├── turtle.cpp
│ ├── turtle_frame.cpp
│ ├── turtlesim
│ │ └── __init__.py
│ └── turtlesim.cpp
├── srv
│ ├── Kill.srv
│ ├── SetPen.srv
│ ├── Spawn.srv
│ ├── TeleportAbsolute.srv
│ └── TeleportRelative.srv
└── tutorials
├── draw_square.cpp
├── mimic.cpp
└── teleop_turtle_key.cpp
9 directories, 41 files
ros2：
│ ├── draw_square.launch.py
│ ├── multisim.launch.py
│ └── __pycache__
│ └── draw_square.launch.cpython-36.pyc
10 directories, 42 files
這裡并未在ros2中添加對應2代版本小烏龜的圖檔。
編譯環節：
ros1：catkin build
ros2：colcon build
指令使用：
rosrun, rostopic ……
ros2 run, ros2 topic ……
具體介紹如下：
ros2 is an extensible command-line tool for ROS 2.
optional arguments:
-h, --help show this help message and exit
Commands:
action Various action related sub-commands
component Various component related sub-commands
daemon Various daemon related sub-commands
launch Run a launch file
lifecycle Various lifecycle related sub-commands
msg Various msg related sub-commands
multicast Various multicast related sub-commands
node Various node related sub-commands
param Various param related sub-commands
pkg Various package related sub-commands
run Run a package specific executable
security Various security related sub-commands
service Various service related sub-commands
srv Various srv related sub-commands
topic Various topic related sub-commands
Call `ros2 <command> -h` for more detailed usage.
對于ros1而言，啟動小烏龜并鍵盤遙控，需要如下步驟：
roscore
rosrun turtlesim turtlesim_node
rosrun turtlesim turtle_teleop_key
類比與ros2，我們可以使用如下指令：
roscore注意ros2無需core
ros2 run turtlesim turtlesim_node
ros2 run turtlesim turtle_teleop_key
非常容易了解。
比如畫一個大圓：
ros2 topic pub /turtle1/cmd_vel ometry_msgs/msg/Twist "{linear: {x: 0.8, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.2}}"