shell.c

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

#define MAX_LINE_LEN 4096
#define MAX_ARGS_LEN 200

int chop(char *str)
{
  const char c[] = "\0";
  int len = strlen(str);
  strcpy(str + len - 1, c);

  return 0;
}

int split(char *str, char *words[], const char *delim)
{
  int len;
  char *cp;
  cp = str;
  for (len = 0; len < MAX_ARGS_LEN; len++) {
    if ((words[len] = strtok(cp, delim)) == NULL)
      break;
    cp = NULL;
  }

  return 0;
}

int main(int argc, char *argv[])
{
  pid_t pid;
  char buf[MAX_LINE_LEN];
  char *words[MAX_ARGS_LEN];

  int i = 5;
  while(i--) {
    printf("> ");
    fgets(buf, sizeof buf, stdin);
    chop(buf);
    if (strlen(buf) == 0) // just pressed return
      continue;
    split(buf, words, " "); // last element of words is NULL

    pid = fork();
    if (pid < 0) {
      printf("fork(2) failed\n");
      exit(1);
    }
    if (pid == 0) { // child process
      execv(words[0], words);
      perror(buf);
      exit(99);
    }
    else { // parent process
      waitpid(pid, NULL, 0);
    }
  }
  printf("bye!\n");

  return 0;
}