opSys-shell/main.c

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

#include "scanner.h"
#include "shell.h"
#include "cmd.h"

// general TODO:
// * properly bind stdin/stdout for piped commands
// * run chains in bg if given '&'
// * manage < and > redirects
// * signal handling
// * builtins - 'kill'

/**
 * This function skips one COMMAND, including redirects and pipes (if any).
 * This is used to move to the next command when a COMPOSITION operator fails.
 * @param lp ListPointer containing remaining Tokens,
 */
void skipCommand(List *lp) {
  *lp = (*lp)->next;
  while (*lp != NULL) {
    switch ((*lp)->type) {
      case PIPELINE:
      case REDIRECT:
      case FILENAME:
      case OPTION:
      case EXECUTABLE:
      case BUILTIN:
        *lp = (*lp)->next;
        break;
      case COMPOSITION:
      case BACKGROUND:
        *lp = (*lp)->next;
        return;
      }
  }
}

/**
 * This function checks whether the current COMPOSITION operator passes (and thus should execute the next function).
 * @param s the COMPOSITION operator.
 * @param status the exit status of the last ran command.
 * @return whether the COMPOSITION succeeds/whether to execute the next command.
 */
bool compositionPasses(char *s, int status) {
  if (!strcmp(s, "&&") && ! status) return true;
  else if (!strcmp(s, "||") && status) return true;
  else if (s[0] == ';' || s[0] == '\n') return true;

  return false;
}

/**
 * Driver function. Contains the main loop which collects and parses input, and decides what and how to execute + output.
 */
int main(int argc, char *argv[]) {
  char *inputLine;
  List tokenList;
  int status = 0;
  bool do_loop = true;
  #if EXT_PROMPT
    bool debug = false;
    char cwd[101], *usr;
  #endif

  // Disable buffering so we don't have to deal with out-of-order prints.
  setbuf(stdin, NULL);
  setbuf(stdout, NULL);

  // The main loop body. Each iteration means one line of input.
  // Will run until either EOF or the BUILTIN exit is given.
  while (do_loop) {
    #if EXT_PROMPT
      getcwd(cwd, sizeof(cwd));
      usr = getlogin();
      if (!status) printf("\x1b[33m%s \x1b[36m%s \x1b[32m>\x1b[0m ", usr, cwd);
      if ( status) printf("\x1b[33m%s \x1b[36m%s \x1b[31m>\x1b[0m ", usr, cwd);
    #endif
    inputLine = readInputLine();
    // We have modified the readInputLine function to return NULL on EOF.
    if (inputLine == NULL) {
      do_loop = false;
      break;
    }
    tokenList = getTokenList(inputLine);

    // Because lists are pointers, we need copies so we can access the list later.
    List cpy = tokenList, og = tokenList;
    if (parseInputLine(&tokenList) && tokenList == NULL ) {
      #if EXT_PROMPT
        if (debug) printList(cpy);
      #endif
      // Consume the entire tokenList (through cpy).
      while (cpy != NULL) {
        switch (cpy->type) {
          // A BUILTIN needs to be executed slightly differently than a COMMAND: 
          // BUILTINS cannot be redirected/piped.
          case BUILTIN:;
            Command cmd = buildCommand(&cpy);
            // If execcuteBuiltin returns false, the BUILTIN was 'exit' and we should stop the shell.
            #if EXT_PROMPT
              if (! executeBuiltin(cmd, &status, &debug)) {
            #else
            if (!executeBuiltin(cmd, &status)) {
            #endif
              do_loop = false;
              cpy = NULL;
            }
            freeCommand(cmd);
            break;

          // Finding an EXECUTABLE means we need to construct the appropriate chain (in case of redirects/pipes), and then run it.
          case EXECUTABLE:;
            Chain chain = buildChain(&cpy);
            #if EXT_PROMPT
            if (debug) printChain(chain);
            #endif
            executeChain(chain, &status);
            freeChain(chain);
            // Status 127 is returned when an EXECUTABLE cannot be found. This requires an extra line to stdout.
            if (status == 127) {
              printf("Error: command not found!\n");
            }
            break;

          // Upon finding a COMPOSITION, we check if it succeeds. if yes, we consume the operator and continue.
          // If not, we skip the next command entirely.
          case COMPOSITION:;
            if (compositionPasses(cpy->t, status)) {
              cpy = cpy->next;
            } else {
              skipCommand(&cpy);
            } 
            break;

          // Encountering any of BACKGROUND, OPTION, PIPELINE, REDIRECT, or FILENAME here means either we are dealing with incorrect syntax,
          // or a function did not correctly consume tokens.
          case BACKGROUND:
          case OPTION:
          case PIPELINE:
          case REDIRECT:
          case FILENAME:
            printf("Error: invalid syntax!\n"); 
            cpy = NULL;
            break;
          }
      }
    } else {
      // If tokenList was not parsed successfully, the syntax must be incorrect.
      printf("Error: invalid syntax!\n");
    }

    // Memory.
    free(inputLine);
    freeTokenList(og);
  }
    
  return 0;
}