// code snippets for the first part of the gosh shell project:
//   - printing the prompt in interactive mode
//   - getting lines of input
//   - properly tokenizing each line
//   - terminating cleanly when end-of-file is received.  this is
//     ctrl-d in interactive mode
//   - replacing keyboard input with file input when in batch mode


// include files I've used so far
#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <assert.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


char *line;
size_t n;
char *token;
int len;
char *nxt;


line = NULL;
n = 0;
// get line of input from stdin.  getline() allocates the buffer
// to store the line
len = getline(&line, &n, stdin);
// getline() return -1 on error.  If errno is 0, the "error" is that
// end-of-file has been reached
if (len == -1 && errno == 0)


// strsep() manipulates it first argument.  So that we can properly free
// the buffer later, copy its address to nxt and have strsep() manipulate
// nxt
nxt = line;
// tokenize the line of input.  the delimiters are space, tab, and newline
// characters
token = strsep(&nxt, " \t\n");
// if delimiter characters are repeated, zero-length tokens will be
//returned.  these tokens should be ignored
if (strlen(token) > 0)
// when finished with the line of input, free the buffer
free(line);


// if we're processing a batch file, (try to) open the file and replace
// stding with the file's file descriptor
int fd = open(argv[1], O_RDONLY);
dup2(fd, STDIN_FILENO);
// the file will now be accessed through stdin.  close the duplicate
// descriptor
close(fd);