SHELL:

INTERNAL COMMANDS: Cd - changes the current working directory L: symbolic components are handled in the directory before dot-dot (“..”) components. P: symbolic components are handled in the directory after dot-dot (“..”) components. echo - writes the arguments to the standard output n: trailing newline character is not printed help: displays the help message and usage pwd - prints the name of the current working directory L: symbolic links are not avoided P: symbolic are avoided

EXTERNAL COMMANDS: cat - read the contents of the file and prints its contents on the standard output n: number all output lines E: display the $ sign at the end of each line date - prints the system’s date and time u: prints Coordinated Universal Time (UTC) R: prints date and time in RFC 5322 format ls - list the contents of the directory a: does not ignore system files (starting from “.”) A: ignores system files (starting from “.”) mkdir - this command makes directories v: prints a message for each created directory m: sets the file mode rm - removes files i: prompt before every file removal v: explains what is being done and which file is being removed

EDGE CASES HANDLED: cd: No such file or directory Invalid command

Echo:
  Invalid command
  Option not present

Pwd:
  Invalid command
  Error

Cat:
  Missing operand
  No file or directory

Date:
  Error
  Invalid command

Ls:
  No such file or directory
  Missing operand

Mkdir:
  Cannot create directory
  Missing operand

Rm:
  Cannot remove file
  Missing operand

THREADING: Type &t after command name (cat &t -n [file name])

TEST CASES: cat -n (filename) cat -E (filename) date -u date -R ls -a mkdir -v (directory name) rm -i (filename) cd -P (directory name) pwd -L Etc.