Ls stands for the List, this command is used to show the information about files and directories
It shows the list of files in your current working directory
-a option is used to show the list of all files including hidden files.
The –l option used to show the “long listing” of information about the files and directories.
The –al option used to show the “long listing” of information about the all files and current directories
The –al/usr shows the list long information about all files in the “/usr” directory
This command lists long information about all files in the “/user” directory and all sub directories and the –R options refer the ls command to give the recursive listing
This command lists information about the /usr directory
This command is very useful when you want to check the permission of the directory