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What do you see when you execute "pipe1" and  Why? Modify the program pipe1.cpp to pipe1a.cpp so that it accepts a command (e.g. "ls -l") from the keyboard. For example, when you execute "./pipe1a ps -auxw", it should give you the same output as pipe1.cpp. Please explain what you changed and why. (Hint: Use string functions strcpy() and strcat() to store the commands in a buffer. Your main function should be like: int main(int argc, char *argv[])) //pipe1.cpp #include #include #include #include #include   using namespace std;   int main() {   FILE *fpi; //for reading a pipe     char buffer[BUFSIZ+1]; //BUFSIZ defined in      int chars_read;   memset (buffer, 0,sizeof(buffer)); //clear buffer   fpi = popen ("ps -auxw", "r"); //pipe to command "ps -auxw"   if (fpi != NULL) {     //read data from pipe into buffer     chars_read = fread(buffer, sizeof(char), BUFSIZ, fpi);       if (chars_read > 0)       cout << "Output from pipe: " << buffer << endl;     pclose (fpi); //close the pipe     return 0;    }     return 1; }

What do you see when you execute "pipe1" and  Why? Modify the program pipe1.cpp to pipe1a.cpp so that it accepts a command (e.g. "ls -l") from the keyboard. For example, when you execute "./pipe1a ps -auxw", it should give you the same output as pipe1.cpp. Please explain what you changed and why. (Hint: Use string functions strcpy() and strcat() to store the commands in a buffer. Your main function should be like: int main(int argc, char *argv[])) //pipe1.cpp #include #include #include #include #include   using namespace std;   int main() {   FILE *fpi; //for reading a pipe     char buffer[BUFSIZ+1]; //BUFSIZ defined in      int chars_read;   memset (buffer, 0,sizeof(buffer)); //clear buffer   fpi = popen ("ps -auxw", "r"); //pipe to command "ps -auxw"   if (fpi != NULL) {     //read data from pipe into buffer     chars_read = fread(buffer, sizeof(char), BUFSIZ, fpi);       if (chars_read > 0)       cout << "Output from pipe: " << buffer << endl;     pclose (fpi); //close the pipe     return 0;    }     return 1; }

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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  • What do you see when you execute "pipe1" and  Why?
  • Modify the program pipe1.cpp to pipe1a.cpp so that it accepts a command (e.g. "ls -l") from the keyboard. For example, when you execute "./pipe1a ps -auxw", it should give you the same output as pipe1.cpp. Please explain what you changed and why.
    (Hint: Use string functions strcpy() and strcat() to store the commands in a buffer. Your main function should be like: int main(int argc, char *argv[]))

//pipe1.cpp

#include <unistd.h>

#include <stdlib.h>

#include <string.h>

#include <stdio.h>

#include <iostream>

 

using namespace std;

 

int main()

{

  FILE *fpi; //for reading a pipe

 

  char buffer[BUFSIZ+1]; //BUFSIZ defined in <stdio.h>

  

  int chars_read;

  memset (buffer, 0,sizeof(buffer)); //clear buffer

  fpi = popen ("ps -auxw", "r"); //pipe to command "ps -auxw"

  if (fpi != NULL) {

    //read data from pipe into buffer

    chars_read = fread(buffer, sizeof(char), BUFSIZ, fpi);  

    if (chars_read > 0) 

     cout << "Output from pipe: " << buffer << endl;

    pclose (fpi); //close the pipe

    return 0; 

  }

 

  return 1;

}

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