How to fix Shell program - c++

Question

the last two days I've been trying to come up with a suitable solution to make this shell simulator that executes linux command run with fork(), dup2(), close(), pipes() and wait() functions. Up to now I have achieved an implementation that leaves me unsatisfied because I have been able to execute a command but I can't get the information from the stdout to be passed to a following command by means of pipes, for example, when writing ls 'l | wc, it would be possible to execute the first command, second of the second that will be carried out according to the information obtained with the first. I would appreciate if someone could clarify what the error in my code is so that I can implement something that allows me to enter a sequence of more than 3 commands that can share their information through the pipe line and print a final result. :)
#include <errno.h> //presentan un informe de error
#include <iostream> //Emplear cin cout c++
#include <stdio.h> //librería estandar de entrada y salida
#include <string.h> //Para manejo de strigs
#include <sys/types.h> // obtener información sobre ficheros
#include <sys/wait.h> //permite el uso de wait
#include <unistd.h> //para poder llamar fork
using namespace std;
// Strig processor
int strProcessor(char *words[50]) {
char command[500]; // Array of char that recieves a full command line
cout << "myshell$"; // print specified value
cin.getline(command, 500); // getline instead of simple cin to read spaces
char *word =
strtok(command, " "); // Pointer for each token starting at the first one
int index = -1;
while (word != NULL) { // Iterate the array to save each string
index += 1; // increase the number of the index
words[index] = word; // Inicialize the each necessary space
word = strtok(NULL, " "); // Save next string of the pointer
}
return index; // Return index because it will be important for later on
}
// Single command processor
int splitCommand(char *words[50], char *singleCommand[50], int index, int start) {
int newIndex = 0; //aux
while (start <= index && strcmp(words[start], "|")) {
singleCommand[newIndex] = words[start];
start += 1;
newIndex += 1;
}
start += 1;
singleCommand[newIndex] = NULL;
return start;
}
//Count the number of commands
int commandCounter(char *words[50], int index){
int counter = 1;
for(int i=0;i<=index;i++) {
if (!strcmp(words[i],"|") && i != index) {
counter += 1;
}
}
return counter;
}
int process(){
int READ = 0;
int WRITE = 1;
int fd[20][2]; // file directory for pipe
int index = -1; // useful index
char *words[50]; // Save all tokens in an array
int start = 0; // useful index
char *singleCommand[20]; // Save an individual command with NULL at the end
//Handling no command written
while (index == -1) {
index = strProcessor(words);
}
//Exit if user types it
if (!strcmp(words[0], "exit")) {
return 0;
}
//Establish the number of commands to exe
int commandNumber = commandCounter(words, index);
//Create a piper for each command
for (int i = 0; i < commandNumber - 1;i++) {
pipe(fd[i]);
}
for (int i = 0; i < commandNumber;i++) {
start = splitCommand(words, singleCommand, index, start); // Get first command
int pid=fork();
if (pid == 0) {
if (i == 0) {
dup2(fd[i][1], STDOUT_FILENO);
close(fd[i][1]);
close(fd[i][0]);
execvp(singleCommand[0], singleCommand);
} else if (i > 0) {
dup2(fd[i-1][0], STDOUT_FILENO);
close(fd[i-1][1]);
close(fd[i-1][0]);
dup2(fd[i][1], STDOUT_FILENO);
close(fd[i][1]);
close(fd[i][0]);
execvp(singleCommand[0], singleCommand);
}
} else {
if (i == 0) {
int stat;
wait(&stat);
close(fd[i][1]);
close(fd[i][0]);
cout << "Process: " << pid << " exits with status:" << stat << endl;
} else if (i > 0) {
int stat;
wait(&stat);
wait(&stat);
close(fd[i-1][1]);
close(fd[i-1][0]);
close(fd[i][1]);
close(fd[i][0]);
cout << "Process: " << pid << " exits with status:" << stat << endl;
}
}
}
return 0;
}
int main() {
process();
return 0;
}
Example input:
ls -alF / | grep bin | cat -n
The displayed messages of the shell should be like:
Process 16480 exits with 0
Process 16481 exits with 0
1 drwxr-xr-x 2 root root 4096 Mar 30 04:07 bin/
2 drwxr-xr-x 2 root root 12288 Mar 30 04:07 sbin/
Process 16482 exits with 0
ls -alF / | grep bin | tr a-z A-Z | rev | cat -n
The displayed messages of the shell should be like:
Process 16554 exits with 0
Process 16555 exits with 0
Process 16556 exits with 0
1 /NIB 70:40 03 RAM 6904 TOOR TOOR 2 X-RX-RXWRD
2 /NIBS 70:40 03 RAM 88221 TOOR TOOR 2 X-RX-RXWRD
Process 16557 exits with 0
Process 16558 exits with 0