====== Directory and File Management ======
List directory contents: 
  ls
Change directory: 
  cd
Print working directory: 
  pwd
Create directory: 
  mkdir
Remove directory: 
  rmdir
Copy files/directories: 
  cp
Move/rename files/directories: 
  mv
Concatenate and display file content: 
  cat
Create empty file: 
  touch
Remove files/directories: 
  rm
Find files in the system: 
  find
Locate a command: 
  which
Estimate file space usage: 
  du
Report file system disk space usage: 
  df