Replicate in C++, in Unix, this command: ps -A | grep argv[1] | wc -l

[kingfisher01]

Hi,

I'm in unix trying to code a c++ program to replicate this command:

ps -A | grep argv[1] | wc -l.

Here is what I have, which doesn't work, and I'm totally lost. Can anyone please help me ? !!!!!!!!!!!!!!! !!!!!!!!!!!!!!! !!!!!!

#include <iostream>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>


using namespace std;

int main(int argc, char *argv[])
{
int pid,pid1,pid2;
int a[2];
int rv;
pipe(a);


if ((pid = fork() == 0))
{

if ((pid1 = fork() == 0))
{

dup2(a[1],1);
close(a[1]);
close(a[0]);

if ((pid2 = fork()) == 0)
{

dup2(a[1],1);
close(a[1]);
close(a[0]);
execlp("/bin/ps","ps","-A",NULL);
}
else
{
dup2(a[0],0);

close(a[1]);
close(a[0]);
execlp("/bin/grep" , "grep" ,argv[1], NULL );
}

}
cout << "back to child" << endl;
execlp("/usr/bin/wc" , "wc" , "-l", NULL );
}
else
{
wait(&rv);
}


return 0;
}

[weaknessforcats]

if ((pid = fork() == 0))              <<?
{
 
if ((pid1 = fork() == 0))             <<?
{
 
etc...
 
if ((pid2 = fork()) == 0)
{

I didn't look at the logic butin the fist two cases, the == operator will execute first due to its higher precedance than the = operator.

The last case looks right.