#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>

bool beginswith(char * big, char * little)
{ for (int i=0; true; i+=1)
  { if (little[i] == 0)
      return true;
    if (little[i] != big[i])
      return false; } }

void main()
{ char pattern[1000], line[1000];
  printf("prefix: ");
  fgets(pattern, 999, stdin);
  int len = strlen(pattern);
  pattern[len-1] = 0;

  int connect[2];
  pipe(connect);

  int p = fork();
  printf("[p=%d, i am %d]\n", p, getpid());

  if (p == 0)
  {
    close(1);
    dup(connect[1]);
    execlp("ls", "ls", NULL);

    fprintf(stderr, "I got execlp wrong\n");
    exit(1);
  }

  FILE * fin = fdopen(connect[0], "r");
  while (true)
  { char * s = fgets(line, 999, fin);
    if (s == NULL)
      break;
    if (beginswith(line, pattern))
      printf("match: %s", line); }

  int s;
  p = wait(& s);
  printf("[done, p=%d, s=%d]\n", p, s); }