README file

Operating Systems and Networks Assignment 2 by Ishan Kavathekar (2022121003) for CS3.301

Instructions to use

Run the makefile using the make command.
Run the ./shell command to run the shell.
User can delete executable file using make clean command.
User can exit the shell using exit command or CTRL+D
The directory in which it is executed will be its home directory.

Specifications

Specification 1:Display requirement

The shell displays the username and hostname in the prompt.
User can input any command from prompt

Specification 2:Builtin commands

cd command:

cd command is used to directory to a specific directory. Various different variations of cd supported in the shell.
cd: changes directory to the home direcotry.
cd . :changes directory to current working directory.
cd .. : changes directory to parent directory.
cd - : changes directory to previous directory.
cd ~ : changes directory to the home direcotry.

echo command:

echo command is used to output the string received by the user.
echo : prints nothing
echo {text} : prints the text after removing any extra tabs and spaces.

pwd command:

pwd command returns the path of the current working directory.

Specification 3: ls command

The ls command prints all the directories, files and executable files in the specified directory, file or executable.
ls command takes two flags: -a and -l
-a flag: This flag also outputs the hidden files and folders.
-l flag: This flag outputs all the details of the files and folders in long format.

Specification 4: System commands with and without arguments

-The shell shoudl alsoexecute all commands like gedit, sleep and emacs.

These commands can either executed in foreground or in the background.
Any command ending with an '&' symbol is treated as a background command.
Else it is considered as a foreground command.

Specification 5:pinfo command

This command prints all the information about the given pid.
The information printed is the pid, the status(running,sleep or zombie), memory and the executable path.

Specification 6: Finished background process

This command prints if the background process exits normally or not.

Specification 7: Discover command

discover command is a user defined command which outputs all the directories and files in the specified directory or file.
This command takes two flags: -d and -f.
-d flag: Searches for all directories.
-f flag: Searches for all files.

Specification 8:History command

history command outputs the last 10 commands given by the user.
history command stores 20 commands but outputs only the latest 10 commands.

Input Output Redirectoin

is used for output redirection
< is used for input redirection
is used to append to the file
It is assumed that the user will enter whitespace after every word.

Command Pipeline

Pipes used to communicated between processes

Jobs

Lists all the jobs according to the flags.
jobs -r : lists all the running jobs.
jobs -s : lists all the stopped jobs.

sig command

sig command takes two arguments: the process number and signal number.
It executes the signal number on the given process.

fg command

Brings background process corresponding to job number to the foreground.
It throws an error if the given job number does not correspond to a valid job number.

bg command

Changes state of stopped background job in running in the background.
It throws an error if the given job number does not correspond to a valid job number.

CTRL-Z

Pushes currrntly executing foreground job to background and changes it's state to stopped.

CTRL-C

Interrupts any ongoing foreground process by sending it the SIGINT signal.

Assumptions

The commands will be of maximum length 200.