ldd is used to print a list of shared libraries that a program or library file depends on

This is a Linux command line instruction that combines two commonly used commands lddand grep. Let me explain it to you one by one:

1. ldd : This is a Linux tool used to print a list of shared libraries that a program or library file depends on. Usually, when you have an executable and want to know which dynamic libraries it links to, you can use lddto see.

   For example, all shared libraries this program depends on ldd lidar_to_pcdwill be listed .lidar_to_pcd

2. | : This is a pipe symbol. It takes the output of the command on the left as input to the command on the right. This is a very common method for combining multiple commands in Unix and Linux systems.

3. grep : This is a command line tool for text search. You can use this to search for lines containing specific text or patterns.

   Here, grep "pcl"we are searching for lines containing the string "pcl".

So the entire command ldd lidar_to_pcd | grep "pcl"means: "List lidar_to_pcdall shared libraries that depend on it, and show only those lines that contain the "pcl" string." This is often used to quickly check whether a program links to a specific library, such as PCL (Point Cloud Library).