OSN Assignment 2

Bachina Venkata Sai Pranav | 2021101116

Requirements

• GCC compiler
• Linux OS (preferably Ubuntu)

Running Shell

From the root directory of project, run make followed by ./shell

File & Functions

Supporting Files

Files containing functions required for proper functioning of the shell.

• shell.c

  • Run Shell Loop
  • Extract Arguments from command
  • Bind functions from different files together

• history.c

  • Adds command to history
  • Stores maximum 20 commands
  • Outputs latest 10 commands

Command Files

Files containing functions to run a particular command.

• echo.c

  • Prints user input after removing excess spaces/tabs

• cd.c

  • Navigate to different directories

• ls.c

  • Prints all files/sub-directories in a location
  • Flags implemented: a and l
  • Multiple directories supported

• pinfo.c

  • Prints info about process with given PID (current process if none is given)

• history.c

  • Prints last n commands, where n is the number given or 10.

• discover.c

  • The command searches for files in a directory hierarchy.

Other Implementations

Commands/functions which don't have a separate file.

• Exiting from the Shell
  • Ctrl+D or Ctrl+C on an empty prompt.

Assumptions

• I submitted two files. One of them has a modularised code and the other one is not.

• Reasonable assumptions are made for things like length of current path, number of commands, command length, etc. The shell will work perfectly for all "day to day work".

• user and hostname will be constant throughout the life of current shell instance.

• echo will treat everything as normal character.

• File and directory names shouldn't contain spaces or special characters. (Some commands may work even without this.)

• pinfo may break on systems not running Ubuntu. This command uses /proc files which may not be same for other OS.quit command.

• Every user input will be stored as it is in history, given it is not same as the last input and contains at least one character other than space or tab.

• Prompt will display only terminated normally or terminated abnormally when a background process ends.

• Prompt will check exist status of background processes only after user inputs a command (possibly empty). The same happens in actual Bash shell.

• Any error while running a command will result in aborting the command after printing an error message.

• & (used for running process in background) can come anywhere in command.

• A hidden file (.history) is used to store history in a readable format. Any changes explicitly done in this file may result in unexpected output of history command.

Customised-C-Shell