OS Assignment 2 MyShell to do file operations

TheLazyBusyCoder's Blog

Welcome to my coding adventures! In this post, we'll explore a C program.

Write a C program to implement the toy shell. It should display the command prompt “myshell$”.

• Tokenize the command line and execute the given command by creating the child process.
• Additionally it should interpret the following commands.
• count c filename :- To print number of characters in the file.
• count w filename :- To print number of words in the file.
• count l filename :- To print number of lines in the file.

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

// seperate sentence: "count c filename" => count , c , filename
void make_toks(char *s, char *tok[])
{
  int i = 0;
  char *p;
  p = strtok(s, " ");
  while (p != NULL)
  {
    tok[i] = p;
    p = strtok(NULL, " ");
    i++;
  }
  tok[i] = NULL;
}

void count(char *fn, char op)
{
  int fh, cc = 0, wc = 0, lc = 0;
  char c;
  fh = open(fn, O_RDONLY);
  if (fh == -1)
  {
    printf("File %s not found.\n", fn);
    return;
  }

  while (read(fh, &c, 1) > 0)
  {
    if (c == ' ')
      wc++;
    else if (c == '\n')
    {
      wc++;
      lc++;
    }
    cc++;
  }

  close(fh);

  switch (op)
  {
  case 'c':
    printf("No.of characters: %d\n", cc);
    break;
  case 'w':
    printf("No.of words: %d\n", wc);
    break;
  case 'l':
    printf("No.of lines: %d\n", lc);
    break;
  }
}

int main()
{
  char buff[80], *args[10];
  int pid;
  int status;
  while (1)
  {
    printf("myshell$ ");
    fflush(stdin);
    fgets(buff, 80, stdin);
    buff[strlen(buff) - 1] = '\0';
    make_toks(buff, args);
    if (strcmp(args[0], "count") == 0)
      count(args[2], args[1][0]);
    else
    {
      pid = fork();
      if (pid > 0)
        wait(&status);
      else
      {
        if (execvp(args[0], args) == -1)
          printf("Bad command.\n");
      }
    }
  }
  return 0;
}