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

int main(int argc, char * argv[])
{ if (argc != 2)
  { fprintf(stderr, "usage: a.out uid\n");
    exit(1); }
  int wanted = atoi(argv[1]);
  FILE * f = fopen("/etc/passwd", "r");
  if (f == NULL)
  { fprintf(stderr, "Can't open /etc/passwd\n");
    exit(1); }
  while (1)
  { char line[1000];
    char * s = fgets(line, 999, f);
    if (s == NULL)
      break;
    if (line[0] == '#')
      continue;
    char * uname = strtok(line, ":\n");
    char * star = strtok(NULL, ":\n");
    int uid = atoi(strtok(NULL, ":\n"));
    char * gid = strtok(NULL, ":\n");
    char * name = strtok(NULL, ":\n");
    char * home = strtok(NULL, ":\n");
    char * shell = strtok(NULL, ":\n");
    if (uid == wanted)
    { printf("%s '%s' %s\n", uname, name, shell);
      break; } }
  fclose(f); }