ROS 学习|查找、安装、卸载、删除功能包|发布和订阅整数/浮点数/布尔/字符串消息|为 .py 文件添加可执行权限

携手创作，共同成长！这是我参与「掘金日新计划 · 8 月更文挑战」的第9天。

前言

本文总结了自己在ROS开发过程中的一些小技巧和经验，东西比较碎，但都蛮实用的。以上，Enjoy~~~

查找、安装、卸载删除某个功能包

在运行别人的demo时，是不是会出现找不到功能包的情况。所以查找、安装和卸载某个功能包是蛮重要的。

查找

查询当前安装完成的所有包文件

 rospack  list

查询ros的所有功能包

 apt-cache search ros-kinetic

或者说在不知道要安装功能包的确切名字的情况下找到目标包

 apt-cache search ros-kinetic | grep rqt-

通过管道线 与grep命令， 输出与关键字rqt-相关的行

再或者下述安装命令与Tab键结合

sudo apt-get install ros-kinetic-rqt-

系统输出相应提示。

安装

安装某个ros包，kinetic要切换为自己的ros版本，比如melodic等。**处时自己索要安装的pkg的名字，这里注意大小写

sudo apt-get install ros-kinetic-**  // 将中间的kinetic换成自己的ros版本

卸载

卸载某个功能包:与安装类似，ros-版本名称-功能包名称。

 sudo apt-get purge ros-kinetic-**  // 将中间的kinetic换成自己的ros版本

最后想要删除的更干净的话，可以删除包的依赖项：

sudo apt-get autoremove

发布和订阅整型/浮点型/布尔型/字符串消息

需要用ROS发布一个布尔类型的消息，上手敲代码的时候竟然不知道具体改用什么数据类型的消息，查找了资料才弄清楚，再这里记录一下

话题消息类型

ROS中的std_msgs包含几乎全部基础的数据类型，包括布尔型，整型，字符串等等。可用rosmsg show std_msgs

std_msgs/Bool
std_msgs/Byte
std_msgs/ByteMultiArray
std_msgs/Char
std_msgs/ColorRGBA
std_msgs/Duration
std_msgs/Empty
std_msgs/Float32
std_msgs/Float32MultiArray
std_msgs/Float64
std_msgs/Float64MultiArray
std_msgs/Header
std_msgs/Int16
std_msgs/Int16MultiArray
std_msgs/Int32
std_msgs/Int32MultiArray
std_msgs/Int64
std_msgs/Int64MultiArray
std_msgs/Int8
std_msgs/Int8MultiArray
std_msgs/MultiArrayDimension
std_msgs/MultiArrayLayout
std_msgs/String
std_msgs/Time
std_msgs/UInt16
std_msgs/UInt16MultiArray
std_msgs/UInt32
std_msgs/UInt32MultiArray
std_msgs/UInt64
std_msgs/UInt64MultiArray
std_msgs/UInt8
std_msgs/UInt8MultiArray

发布话题

这个很基础的操作，注意以下几点就行

• include 相关的头文件
• 消息的类型为Std_msgs::XXX. 消息成员是"data" 示例：

#include "ros/ros.h"
#include "std_msgs/String.h"

#include <sstream>

/**
 * This tutorial demonstrates simple sending of messages over the ROS system.
 */
int main(int argc, char **argv)
{
  /**
   * The ros::init() function needs to see argc and argv so that it can perform
   * any ROS arguments and name remapping that were provided at the command line.
   * For programmatic remappings you can use a different version of init() which takes
   * remappings directly, but for most command-line programs, passing argc and argv is
   * the easiest way to do it.  The third argument to init() is the name of the node.
   *
   * You must call one of the versions of ros::init() before using any other
   * part of the ROS system.
   */
  ros::init(argc, argv, "talker");

  /**
   * NodeHandle is the main access point to communications with the ROS system.
   * The first NodeHandle constructed will fully initialize this node, and the last
   * NodeHandle destructed will close down the node.
   */
  ros::NodeHandle n;

  /**
   * The advertise() function is how you tell ROS that you want to
   * publish on a given topic name. This invokes a call to the ROS
   * master node, which keeps a registry of who is publishing and who
   * is subscribing. After this advertise() call is made, the master
   * node will notify anyone who is trying to subscribe to this topic name,
   * and they will in turn negotiate a peer-to-peer connection with this
   * node.  advertise() returns a Publisher object which allows you to
   * publish messages on that topic through a call to publish().  Once
   * all copies of the returned Publisher object are destroyed, the topic
   * will be automatically unadvertised.
   *
   * The second parameter to advertise() is the size of the message queue
   * used for publishing messages.  If messages are published more quickly
   * than we can send them, the number here specifies how many messages to
   * buffer up before throwing some away.
   */
  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);

  ros::Rate loop_rate(10);

  /**
   * A count of how many messages we have sent. This is used to create
   * a unique string for each message.
   */
  int count = 0;
  while (ros::ok())
  {
    /**
     * This is a message object. You stuff it with data, and then publish it.
     */
    std_msgs::String msg;

    std::stringstream ss;
    ss << "hello world " << count;
    msg.data = ss.str();

    ROS_INFO("%s", msg.data.c_str());

    /**
     * The publish() function is how you send messages. The parameter
     * is the message object. The type of this object must agree with the type
     * given as a template parameter to the advertise<>() call, as was done
     * in the constructor above.
     */
    chatter_pub.publish(msg);

    ros::spinOnce();

    loop_rate.sleep();
    ++count;
  }


  return 0;
}

这是ROS WIKI上的代码，如果看不懂的话，点击这个链接，上面有详细的解析。

订阅话题

同样是基础的操作，注意：

• include 相关头文件
• 回调函数的参数是指针，因此需要用“msg->data”的形式访问话题内容 代码：

#include "ros/ros.h"
#include "std_msgs/String.h"

/**
 * This tutorial demonstrates simple receipt of messages over the ROS system.
 */
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}

int main(int argc, char **argv)
{
  /**
   * The ros::init() function needs to see argc and argv so that it can perform
   * any ROS arguments and name remapping that were provided at the command line.
   * For programmatic remappings you can use a different version of init() which takes
   * remappings directly, but for most command-line programs, passing argc and argv is
   * the easiest way to do it.  The third argument to init() is the name of the node.
   *
   * You must call one of the versions of ros::init() before using any other
   * part of the ROS system.
   */
  ros::init(argc, argv, "listener");

  /**
   * NodeHandle is the main access point to communications with the ROS system.
   * The first NodeHandle constructed will fully initialize this node, and the last
   * NodeHandle destructed will close down the node.
   */
  ros::NodeHandle n;

  /**
   * The subscribe() call is how you tell ROS that you want to receive messages
   * on a given topic.  This invokes a call to the ROS
   * master node, which keeps a registry of who is publishing and who
   * is subscribing.  Messages are passed to a callback function, here
   * called chatterCallback.  subscribe() returns a Subscriber object that you
   * must hold on to until you want to unsubscribe.  When all copies of the Subscriber
   * object go out of scope, this callback will automatically be unsubscribed from
   * this topic.
   *
   * The second parameter to the subscribe() function is the size of the message
   * queue.  If messages are arriving faster than they are being processed, this
   * is the number of messages that will be buffered up before beginning to throw
   * away the oldest ones.
   */
  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);

  /**
   * ros::spin() will enter a loop, pumping callbacks.  With this version, all
   * callbacks will be called from within this thread (the main one).  ros::spin()
   * will exit when Ctrl-C is pressed, or the node is shutdown by the master.
   */
  ros::spin();

  return 0;
}

参考文献

std_msgs ROSWIKI DEMO官方

批量化为.py文件添加可执行权限

在ROS中，想要用rosrun命令运行python文件，首先要对该文件提价可执行权限。如果要是用鼠标一个一个点左键设置属性，效率很低，并且不够优雅～～～可以用chmod命令解决

解决方案

chmod命令用于修改文件的访问权限。该命令有两种用法。一种是包含字母和操作符表达式的文字设定法；另一种是包含数字的数字设定法。 命令格式：chmod [权限] 文件名 文件名可以使用通配符，文件名为星号*表示匹配所有文件。

用法示例： 为/home/zhidao/py目录下的所有文件添加执行权限。 $ chmod +x /home/zhidao/py/* +表示增加权限，r, w, x分别表示可读取、可写入和可执行。