/sce213-pa0-2019f

Primary LanguageC

SCE213 Operating Systems (Fall 2019)

Project #0: Implementing a Command Line Parser

Due on 11:59:59pm, September 20 (Friday)

Introduction

The purpose of this project is to bootstrap the term project of implementing a shell program, and to get familiar with our project 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. A string is defined as a sequence of characters which is terminated with \0. A command token is defined as a sequence of characters without whitespaces, where the whitespaces include spaces(' ') and tab characters('\t').

For example, if the input string is " Hello world ", the command tokes are "Hello" and "world". Note that the tokens do not include any space characters. Another example is for an input string " cp a.out pa0.c /tmp "; it should be broken into "cp", "a.out", "pa0.c", and "/tmp".

This feature should be implemented in parse_command() function. 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/sanghoon ". Note that each token is also a string which is terminated with \0.

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

Skeleton Code

You can start this program assignment by cloning this repository at https://github.com/sslab-ajou/sce213-pa0-2019f. Everything is in pa0.c. Please do not modify the main() function, but implement your code in parse_command() function.

All submission and grading are done automatically through https://sslab.ajou.ac.kr/pasubmit. Please follow the instruction explained in the class. Note that input file in the provided code contains the input sequence for the grading.

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.
  • 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.
  • 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.
  • Submit only the pa0.c file to the submission server at https://sslab.ajou.ac.kr/pasubmit.
  • Report

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 command is scanned. Assign the starting position of each token into tokens[] and count nr_tokens accordingly.
  • 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!