C - SHELL

Mini Project 1 - Operating Systems and Networks, Monsoon 2023

Building and running

Run make in the root directory to build. Run ./a.out to run the shell.

Description

Directory structure

• main.c is the main file which initializes the shell and is the entry point of the program.
• headers.h is the header file which contains all the general function declarations and global variables.
• prompt folder contains the source code for the prompt of the shell.
• utils folder contains the source code for some utility functions required by other files.
• commands folder contains the source code for the commands of the shell.

Usage

• The working directory of the shell is the directory where it was executed from.
• Commands can be chained with ; or &. & is to send the process to the background.
• The symbols <, > and >> are used for input, output and output append redirection respectively.
• We can use | to pipe the output of one command to another.
• Type exit to exit the shell.

Commands

The shell supports the following commands:

Directory	Description	Usage
commands/warp/	Change working directory to a directory specified by the user	warp <path>
commands/proclore/	Print information about a process specified by the user	proclore <pid>
commands/pastevents/	Print the last 15 (at most) commands executed by the user. Also used to clear history or run some previous command	pastevents <purge> / <execute index>
commands/peek/	Print the files and directories present in the given directory	peek <-l> <-a> <path>
commands/activities/	Print a sorted list of all the processes spawed by the shell	activities
commands/neonate/	Continuously prints the pid of the most recently created process of the system at fixed intervals	neonate -n <time_arg>
commands/iMan/	Print the manual for the command given, by using sockets to get the information from the web	iMan <command>

Utilities

The following utility functions are used by other files:

Directory	Description
utils/delimiter/	Achieve tokenization of input string based on a certain delimiter, and return number of tokens, the tokens themselves, etc.
utils/cwd/	Return the current working directory
utils/str_to_num/	Can check if a string is a number, and convert a string to a number
utils/common/	Contains some common useful functions used by other files, such as a safe malloc, error handling, etc.
utils/execute/	The main part of the code which executes all the other commands.
utils/history/	Contains commands to handle storing and retrieving history from the persistent storage.
utils/process/	Contains functions to handle the process list for processes spawed by the shell.
utils/rawmode/	It allows us to toggle back and forth between raw mode and cooked mode.

Assumptions

• If the word pastevents comes anywhere in the command (without the correct usage of pastevents execute <number>), the command will not be included in the history.
• The command peek can include more than one path as well, and will just display the contents of all the paths given one after another. The flags can also come anywhere in the command, and will be handled accordingly.
• The way the input is parsed doesn't take into account quotation marks. Therefore commands like echo print the text along with the quotes.
• iMan only prints NAME, SYNOPSIS and DESCRIPTION for the command given. It doesn't print the other sections. Also, if the length of these exceeds the buffer length of 4096, it truncates it.
• neonate command only takes integer values are valid argument for time.
• After a background process terminates, the display will display the main command name, not the entire command.
• Pipes works with I/O redirection as well. However, custom commands are not involved in the pipe.