Computer Science

CS3376 501/503, Assignment 4

Due Date: submitted to elearning.utdallas.edu by 03/30/2015 at 23:55 pm.

Part1, question1: 50 points, Part1, question2: 50 points, Part2 (optional): 30 points

1. Assignment Learning Outcome:

– How to create a child process – How to use stdin and stdout – How to use pipes

2. Problem Description

Part1 In class, we have seen the following code, that uses pipes and fork() call to implement the shell pipe “|”. The code is following: // file: onepipe.cpp // author: M. Amine Belkoura // date: 03/04/2015 // purpose: CS3376 // description: // this program executes “ls -ltr | grep 3376”, by dividing the two command among the child and parent process #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <sys/types.h> #include <sys/stat.h> int main(int argc, char **argv){ int status; int childpid; char *cat_args[] = {“ls”, “-ltr”, NULL}; char *grep_args[] = {“grep”, “3376”, NULL}; // create one pipe to send the output of “ls” process to “grep” process int pipes[2]; pipe(pipes); // fork the first child (to execute cat) if((childpid = fork()) == -1){ perror(“Error creating a child process”); exit(1); } if (childpid == 0) { // replace cat’s stdout with write part of 1st pipe dup2(pipes[1], 1); // close all pipes (very important!); end we’re using was safely copied close(pipes[0]);

3

close(pipes[1]); execvp(*cat_args, cat_args); exit(0); } else { // replace grep’s stdin with read end of 1st pipe dup2(pipes[0], 0); close(pipes[0]); close(pipes[1]); execvp(*grep_args, grep_args); } return(0); }

Change code to execute the following double pipe command: “ls -ltr | grep 3376 | wc –l” 1- Use one parent and two children to do the work. Call the file TwoPipesTwoChildren.cpp. 2- Write another version where the parent create 3 children, and the children will execute the

commands (parent will do nothing, just lay in the sofa ! ). Call the file TwoPipesThreeChildren.cpp

Part2

In part1, a double pipe is used to execute the command “ls -ltr | grep 3376 | wc –l”. However, our program is static: it means that code need to be modified and rebuilt if we want to change the commands to execute. In this part, we make our program dynamic instead of static. The following requirements should be implemented: 1- Source file will be called DynPipe.cpp, executable called dynpipe. 2- The piped commands to execute need to be passed as arguments to dynpipe,and not hardcoded. 3- The max number of arguments should not exceed 5, and not less than 2 (otherwise print an error

message) 4- Each argument should be a unix/linux command with its parameters. The first argument will be the

first to execute, followed by the second one, etc.. We will assume that only valid commands can be used, for simplicity Example: the followings are possible command executions

Program execution Shell equivalent dynpipe “ls –ltr” “grep 3376” ls –ltr |grep 3376 dynpipe “ls –ltr” “grep 3376” “grep hi” wc -l ls –ltr |grep 3376| grep hi| wc-l dynpipe “ls –ltr” error

3. WHAT TO SUBMIT TO ELEARNING:

1- Write one Makefile for the whole assignment. 2- Use two-step building process in Makefile 3- Submit a simple compressed (zip) file, with all source and Makefile. Zip file should have the

following format format <lastname>_<firstname>_assign2.zip

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