Programming Assignment 0

Programming Assignment 0

ICT332 Operating Systems (Spring 2020)

Project #0: Implementing a Command Line Parser

Due on the end of March 29 (Sunday) (23:59:59)

Introduction

The purpose of this project is to bootstrap the term project to implement a shell program, and to get familiar with the programming assignment submission system.

Problem Specification

We will implement a shell program soon. To that end, you should firstly make the shell program to understand user inputs and commands.

In this project, the framework passes input strings, and your task is to split the input strings into command tokens. By C standard, a string is defined as a sequence of characters which is terminated with \0. Command tokens are strings that are obtained by splitting the input string with delimitors which is whitespace characters in this PA. Use isspace()function to check whether a character is whitespace or not. Any heading and trailing whitespace should be removed from the command tokens.

For example, if the input string is " Hello world ", the command tokes are "Hello" and "world". Note that the input string is split into tokens delimited by whitespaces (' ' in this example), and the tokens do not contain whitespaces.

Another example string is " cp a.out pa0.c /tmp ". It should be broken into "cp", "a.out", "pa0.c", and "/tmp".

Skeleton Code

The required functionality must be implemented in parse_command() function in pa0.c. The user input is passed through command. After parsing command into tokens, the tokens should be assigned to tokens[] in order, which is passed as the argument of the parse_command() function. Also, the number of tokens should be assigined to *nr_tokens which will be used by the framework.

Below diagram illustrates a correct result for an input string " ls -al /home/ict332 ". Note that each token is also a string which is terminated with \0.

char *command --> " ls -al /home/ict332 " *nr_tokens = 3 tokens[0] --> "ls" tokens[1] --> "-al" tokens[2] --> "/home/ict332" tokens[3]... = NULL

Restrictions

You should not use any string manipulation functions from any libraries . The banned functions include strtok, strtok_r, strlen, fscanf and/or similars. This implies that you should implement your own string manipulation functions if it is needed. You will get 0 point if you use any of them . Note that malloc() and free() are not string manipulation functions and OK to use. If unsure, question to TA/professor through AjouBb.

. The banned functions include strtok, strtok_r, strlen, fscanf and/or similars. This implies that you should implement your own string manipulation functions if it is needed. . Note that malloc() and free() are not string manipulation functions and OK to use. If unsure, question to TA/professor through AjouBb. Use isspace() C library function to check whether the character can be assumed as a whitespace.

isspace() C library function to check whether the character can be assumed as a whitespace. Printing messages to stand output (e.g., printf()) is totally OK. However, do not fprintf(stderr ...) otherwise the grading system cannot grade your submission properly.

Logistics

This is an individual project; you work on the assignement alone. You can use up to 4 slip tokens throughout this semester. You can start this program assignment by cloning this repository at https://github.com/sslab-ajou/ict332-pa0-2020s. Everything is in pa0.c. Please do not modify the main() function, but implement your code in parse_command(). You can add any functions or macros if you need, for sure. This is an OS/architecture-independent project; you may use Visual Studio on Windows or vim/gcc on Linux. However, the grading will be done on a Linux machine. So, write code as neutral as possible to compilers. All submission and grading are done automatically through https://sslab.ajou.ac.kr/pasubmit. Please follow the instruction explained in the class. Submit pa0.c file to the PA submission site. (80 pts) Explain your parsing strategy on a 1-page PDF document. Submit the document as the report in the PASubmit. (20 pts) input file in the provided code contains the input sequence for the grading.

Tips and Notes

Briefly speaking, the implementation might look like; start scanning from the beginning of command skipping all whitespaces until meet a non-whitespace character. That will be the beginning of the token. Then, resume scanning until meet any whitespace character (' ' or '\t'). That will be the end of the token. Repeat this until entire commandis scanned. Read comments in the skeleton code carefully. Make sure every string is terminated with '\0'. Post freely on QnA board on AjouBb to question about the project.

Good luck and have fun!

from http://woochan-autobiography.tistory.com/122 by ccl(A) rewrite - 2020-03-18 12:20:25

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