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

#include <sys/types.h>
#include <sys/wait.h>

/* The array below will hold the arguments: args[0] is the command. */
static char* args[512];

/* Modify this function to run commands.
 * 'first' and 'last' are useful when connecting pipes.
 *
 * input: return value from previous command (useful for pipe file descriptor)
 * first: 1 if first command in pipe-sequence (no input from previous pipe)
 * last: 1 if last command in pipe-sequence (no input from previous pipe)
 *
 * EXAMPLE: If you type "ls | grep shell | wc" in your shell:
 *    fd1 = command(0, 1, 0), with args[0] = "ls"
 *    fd2 = command(fd1, 0, 0), with args[0] = "grep" and args[1] = "shell"
 *    fd3 = command(fd2, 0, 1), with args[0] = "wc"
 *
 * So if 'command' returns a file descriptor, the next 'command' has this
 * descriptor as its 'input'.
 */
static int command(int input, int first, int last)
{
  /* Be careful when using 'fork': make sure the child terminates
     (call 'exit' if 'execvp' fails). */	
  int i, commands = 0;

  pid_t pid;
  char *env[] = { "HOME=/usr/home/", "LOGNAME=home", (char *)0 };
  char loc[35] = "";
  int pd[2];

  /* Initialize the pipe */
  if(last == 0) {
    fprintf(stderr,"Pipe created.\n");
    if(pipe(pd) < 0) {
      perror("Creating pipe");
      exit(EXIT_FAILURE);
    }
  }

  pid = fork();
	
  if(pid == 0) { /* Child  */
    /* Redirection and closing of pipes */
    if(first == 1 && last == 0) {
      dup2(pd[1],1);
      close(pd[1]);
    }
    else if(first == 0 && last == 1) {
      dup2(input,0);
      close(input);
      close(pd[0]);
      close(pd[1]);
    }
    else if(first == 0 && last == 0) {
      dup2(pd[1],1);
      close(pd[1]);
      dup2(input,0);
      close(input);
    }
	    
    /* Construct the command */
    strcat(loc,"/bin/");
    strcat(loc,args[0]);
	  
    fprintf(stderr,"command: %s\n", args[0]);
    for (i = 1; args[i] != NULL; i++) {
      commands++;
      fprintf(stderr,"argument %d: %s\n", i, args[i]);
    }
	    
    char *cmd[commands+1];
    for(i = 0; args[i] != NULL; i++) {
      cmd[i] = args[i];
    }
	  
    cmd[commands+1] = (char *)0;
    /* Call the constructed command */
    execve(loc, cmd, env);
    exit(EXIT_SUCCESS);
  }
  else { /* Parent */
    wait(NULL);
    /* IF one single command, return 0 */
    if(first == 1 && last == 1) {
      return 0;
    }
    close(pd[1]);
    if(last == 1) {
      close(input);
      close(pd[0]);
      return 0;
    }
  }

  return pd[0];
}

/* Here you can do some final cleanup, such as 'wait' for
 * processes to terminate.
 *
 *  n : Number of times 'command' was invoked.
 */
static void cleanup(int n)
{
  /* something like this, perhaps: */
  int i;
      for(i = 0; i < n; i++) wait(NULL);
}

/*
 * NOTHING need to be changed below here...
 */

static int run(char* cmd, int input, int first, int last);

static char line[1024];
static int n = 0; /* number of calls to 'command' */

int main()
{
	printf("SIMPLE SHELL: Type 'exit' or send EOF to exit.\n");
	while (1) {
		/* Print the command prompt */
		printf("$> ");
		fflush(NULL);

		/* Read a command line */
		if (!fgets(line, 1024, stdin)) 
			return 0;

		int input = 0;
		int first = 1;

		char* cmd = line;
		char* next = strchr(cmd, '|'); /* Find first '|' */

		while (next != NULL) {
			/* 'next' points to '|' */
			*next = '\0';
			input = run(cmd, input, first, 0);

			cmd = next + 1;
			next = strchr(cmd, '|'); /* Find next '|' */
			first = 0;
		}
		input = run(cmd, input, first, 1);
		cleanup(n);
		n = 0;
	}
	return 0;
}

static void split(char* cmd);

static int run(char* cmd, int input, int first, int last)
{
	split(cmd);
	if (args[0] != NULL) {
		if (strcmp(args[0], "exit") == 0) 
			exit(0);
		n += 1;
		return command(input, first, last);
	}
	return 0;
}

static char* skipwhite(char* s)
{
	while (isspace(*s)) ++s;
	return s;
}

static void split(char* cmd)
{
	cmd = skipwhite(cmd);
	char* next = strchr(cmd, ' ');
	int i = 0;

	while(next != NULL) {
		next[0] = '\0';
		args[i] = cmd;
		++i;
		cmd = skipwhite(next + 1);
		next = strchr(cmd, ' ');
	}

	if (cmd[0] != '\0') {
		args[i] = cmd;
		next = strchr(cmd, '\n');
		next[0] = '\0';
		++i; 
	}

	args[i] = NULL;
}