UNIX for Dummies Questions & Answers

#include <stdio.h>
#include <stdlib.h>

int main (int argc, char *argv[])
{
  FILE *pipein;
  char readbuf[80];

  if ((pipein = popen("ls | grep <myfile>", "r")) == NULL)
  {
    perror("popen");
    exit(1);
  }

  fgets(readbuf, 80, pipein);
  printf("%s", readbuf);

  close(pipein);
  return(0);
}

for(i=0;i<argc;i++){
   
       if(i==0&&argc>1){//first command
           if(pipe(pipa1)==-1)
               perror("pipe");
           if((pid=fork())<0)    
                perror("fork");
            if(pid==0){//child
                printf("jag är fösta kommandot");
                printf("I am a 1 process--%d, my parent is--%d jag skall exikvera--%s\n ",getpid(),getppid(),com[i].argv[0]);
                dupPipe(pipa1, WRITE_END, STDOUT_FILENO);
                execvp(com[i].argv[0],com[i].argv);
            }                
       }
       if (i>0 && argc==2) {       
         pid = fork();          
         if (pid == 0) {        
            printf("jag är andra kommandot");
            printf("I am a process--%d, my parent is--%d jag skall exikvera--%s \n ",getpid(),getppid(),com[i].argv[0]);
            dupPipe(pipa1, READ_END, STDIN_FILENO);
            execvp(com[i].argv[0],com[i].argv);
             }
   
        }

/* Duplicate a pipe to a standard I/O file descriptor, and close both pipe ends
 * Arguments:    pip    the pipe
 *        end    tells which end of the pipe shold be dup'ed; it can be
 *            one of READ_END or WRITE_END
 *        destfd    the standard I/O file descriptor to be replaced
 * Returns:    -1 on error, else destfd
 */
int dupPipe(int pip[2], int end, int destfd){
 
  if (-1 == dup2 (pip[end], destfd))
    {
      perror ("dupPipe()");
      return -1;
    }
  return destfd;
}