ls Common Command-Line Options
Command Use：
ls -l Shows a long listing, which includes information about file properties, such as creation date and permissions.
ls -a Shows all files, including hidden files.
ls -lrt This is a very useful command. It shows commands sorted on modification date. You’ll see the most recently modified files last in the list.
ls -d Shows the names of directories, not the contents of all directories that match the wildcards that have been used with the ls command.
ls -R Shows the contents of the current directory, in addition to all of its subdirectories; that is, it R ecursively descends all subdirectories.