CS 352 - Unix Software Development - Page 2 - Overclock.net

deafboy · 08-22-09

^
I was way off, I'm was going off what I had heard.

After a brief talk with someone that has already taken the course it seems like it wont be an entire kernal from scratch (thank God). I guess it's going to be a 6 part mini-shell. I guess I'll just have to start reading up and see what happens once some of the stuff is posted. After talking about it, it is sounding a lot easier that I thought but it'll definitely keep me busy.

*sigh of relief*

Pooping^fish · 08-23-09

Sounds good dude, keep us posted. If you ever need help, we dont do your homework, but were here.

Ill be interested to see what classes I have interest in when I get where you are. Getting an early start has really helped me so far.

deafboy · 09-30-09

Well we got assigned out first program last week (first day of class nonetheless), and I just turned it in. YAY. lol. It turned out being easier than I thought. I'm definitely still getting used to the unix thing. I definitely need to work on my debugging skills within the terminal. I spent a solid couple hours today looking everything over wondering why it wasnt working. lol. I had a 1 instead of a 0. DOH.

Is it alright if I post my code up here to get your guy's feedback?

lol. All in all I thought I did pretty well for the week. Learned how to use netBSD, the terminal, and wrote a very small portion of the shell. Part 1 down...only 5/6 more. ha.

Code:

/* CS 352 -- Mini Shell!  
 *
 *   Cole Markusen
 *   Programming Assignment 1
 *   Created:  September 24th, 2009 
 *   Modified: September 29th, 2009 
 *
 */

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


/* Constants */ 

#define LINELEN 1024

/* Prototypes */

void processline (char *line);
char** arg_parse (char *line);

/* Shell main */

int
main (void)
{
  char   buffer [LINELEN];
  int    len;

  while (1) {

    /* prompt and get line */
    fprintf (stderr, "%% ");
    if (fgets (buffer, LINELEN, stdin) != buffer)
      break;

    /* Get rid of \n at end of buffer. */
    len = strlen(buffer);
    if (buffer[len-1] == '\n')
      buffer[len-1] = 0;

    /* Run it ... */
    processline (buffer);

  }

  if (!feof(stdin))
    perror ("read");

  return 0;/* Also known as exit (0); */
}


void processline (char *line)
{
  pid_t  cpid;
  int    status;
  char **args;

  args = arg_parse(line);
    
  /* Start a new process to do the job. */
  cpid = fork();
  if (cpid < 0) {
    perror ("fork");
    return;
  }
    
  /* Check for who we are! */
  if (cpid == 0) {
    /* We are the child! */
    execvp(args[0], args); //replace process
    perror ("exec");
    exit (127);
  }

  /* Have the parent wait for child to complete */
  if (wait (&status) < 0)
    perror ("wait");

  free(args); //freeing up memory

}




char** arg_parse (char *line)
{
  char** argv;    //array for arguments
  int count = 0;  //counter for number of arguments
  int i;          //incrementation for 'for loops'
  int index = 0;  //incrementation for array
  int length = strlen(line);  //length of line

  
  for(i=0; i < length; i++)
    {
      if(line[i] != ' ' && (line[i+1] == ' ' || line[i+1] == '\0' || line[i+1] == '\n'))
	{
	  count++; //counting number of arguments
	}
    }

  argv = (char**)calloc(sizeof(char**), count + 1); //allocating size
  
  for(i=0; i < length; i++)
    {
      if(i == 0 && line[i] != ' ')
	{
	  argv[index] = &line[i]; //adding character to array
	  index++;
	}
      if(line[i] == ' ')
	{
	  line[i] = '\0';  //replacing whitespaces with 0.
	
	  if(line[i+1] != ' ' && line[i+1] != '\0')
	    {
	      argv[index] = &line[i+1]; //adding character to array
	      index++;
	    }
	}
    }


  return argv; // returning array

}

deafboy · 10-11-09

So I turned in my second program Friday morning... unfortunately I turned it in incomplete (has bugs).

I was hoping I could get some fresh set of eyes on this to see if anyone can help me fix things up. I hate having incomplete/buggy code

I know some of the logic is a little sketch, didn't get much sleep last week.

The Assignment:
HERE

msh (minishell main)

Code:

/* CS 352 -- Mini Shell!  
 *
 *   Author: Cole Markusen
 *   Assignment Number: 2
 *   Class: CSCI 352 -- Unix Developement
 *   Created:  September 24th, 2009 
 *   Modified: October 9th, 2009 
 *
 *   The heart of this minishell was taken from minishell.c 
 *   created by Phil Nelson.  Function calls for arguments
 *   implemented as well as some error handling
 */

#include "proto.h"




/* Constants */ 

#define LINELEN 1024

/* Prototypes */

void processline (char *line);

/* Shell main */

int
main (void)
{
  char   buffer [LINELEN];
  int    len;

  while (1) {

    /* prompt and get line */
    fprintf (stderr, "%% ");
    if (fgets (buffer, LINELEN, stdin) != buffer)
      break;

    /* Get rid of \n at end of buffer. */
    len = strlen(buffer);
    if (buffer[len-1] == '\n')
      buffer[len-1] = 0;

    /* Run it ... */
    processline (buffer);

  }

  if (!feof(stdin))
    perror ("read");

  return 0;/* Also known as exit (0); */
}


void processline (char *line)
{
  pid_t  cpid;              //Process Identification
  int    status;            //Status of process
  int number_of_parameters; //Number of arguments in the line
  int command_builtin;      //Whether the command is a built in or not,
                            // 0 if it is, -1 if it is not.
  char **args;              //Argument array

  number_of_parameters = arg_parse(line, &args);
  command_builtin = check_builtin(number_of_parameters, args);

  if(command_builtin == -1)
    {
      if (number_of_parameters == 0)
        {
          return; //blank line inputed
        }

      if (number_of_parameters > 0)
        {

          /* Start a new process to do the job. */
          cpid = fork();
          if (cpid < 0) {
            perror ("fork");
            return;
          }
    
          /* Check for who we are! */
          if (cpid == 0) {
            /* We are the child! */
            execvp(args[0], args); //replace process
            perror ("exec");
            exit (127);
          }

          /* Have the parent wait for child to complete */
          if (wait (&status) < 0)
            perror ("wait");

          free(args); //freeing up memory
        }
    }

  if (number_of_parameters == -1)
    { 
      //printin error for unbalanced quotation marks   
      fprintf(stderr, "error: unmatched quotation marks. \n");
      main();
    }

}

arg_parse (argument parser) -- disregard the print_array if you want. I used it to help me debug

Code:

/* CS 352 -- Arg_Parse 
 *
 *   Author: Cole Markusen
 *   Assignment Number: 2
 *   Class: CSCI 352 -- Unix Developement
 *   Created:  October 5th, 2009 
 *   Modified: October 9th, 2009 
 *
 */

#include "proto.h"





void print_array(int count, char** argv, char* line, int pos)
{
  int i = 0;
  printf ("\"%s\"\n ", line);
  for (i = 0; i < pos; i++) {
	printf (" ");
  }
  printf ("^\n");  

  printf ("===============================\n");
  for (i = 0; i < count +1; i++)
    {
      printf("[%i] => \"%s\"\n", i, argv[i]);
    }
  printf ("===============================\n");
  return;
}












//function to shift the entire line to the left
//currently used to get rid of quotes
char* shift(char *line, int length, int i)
{
  int j=0;

  for(j = i; j < length; j++)
    {
      line[j] = line[j+1];
    }

  return line;
}





int arg_parse (char *line, char ***argvp)
{
  char original[1024];
  char** argv;    //array for arguments
  int count = 0;  //counter for number of arguments
  int i;          //incrementation for 'for loops'
  int index = 0;  //incrementation for array
  int length = strlen(line);  //length of line
  int number_of_quotes = 0;   //tally for number of quotes
  bool quotations = false;    //bool to flag whether you're 
                              //inside a quote or not
  strcpy (original, line);


  //count the number of quotes
  for(i=0; i < length; i++)
    {
      if(line[i] == '"')
        {
	  number_of_quotes++;
        }
    }


  //uneven number of quotes -- error
  if((number_of_quotes % 2) != 0)
    {
      return -1;
    }


  //count the number of arguments
  for(i=0; i<length; i++)
  {
    if(line[i] == '"')
      {
        if(quotations == false)
	  {
	    quotations = true; //inside quote
	  }
        else
	  {
	    quotations = false; //leaving quote
	  }
      }

    if(line[i] == ' ' || line[i+1] == '\0')
      {
        if((line[i+1] != ' ' && line[i+1] != '\t') && !quotations)
	  {
	    count++; //increment number of arguments
	  }
      }
  }

  argv = (char**)calloc(sizeof(char**), count + 1); //allocating size


  for(i=0; i<length; i++)
  {
    print_array(count, argv, original, i);
    if(i == 0 && line[i] != ' ' && line[i] != '"' && line[i] != '\t')
      {
	argv[index] = &line[i]; //adding character to array
	index++;
      }

    if(line[i] == '"')
      {
        if(quotations == false)
	  {
	    quotations = true; //inside quote
	  }
        else if (quotations == true && line[i+1] == ' ')
	  {
	    quotations = false; //leaving quote
	  }

	line = shift(line, length, i); //get rid of quotes
	i--;

      }

    if((line[i] == ' ' || line[i] == '\t') && !quotations)
      {
        if(line[i+1] != ' ' && line[i+1] != '\t' && line[i+1] != '\0')
	  {
	    argv[index] = &line[i+1]; //adding character to array
	    index++;
	}

	line[i] = '\0';  //replacing whitespaces with 0.
      }

  }

 

  *argvp = argv; //setting array values
  

  return count; // returning number of parameters

}

builtin (Built In Commands)

Code:

/* CS 352 -- Builtin Functions  
 *
 *   Author: Cole Markusen
 *   Assignment Number: 2
 *   Class: CSCI 352 -- Unix Developement
 *   Created:  October 5th, 2009 
 *   Modified: October 9th, 2009 
 *
 */

#include "proto.h"

//declare typedef function and struct
typedef void(*builtin_ptr)(int, char**);
typedef struct {char *name; builtin_ptr func;} bi_entry;

//declare built in commands
void do_exit(int count, char** args);
void do_aecho(int count, char** args);


//Putting commands into an array and setting the number of commands.
bi_entry commands[] = {{"exit", do_exit}, {"aecho", do_aecho}};
int number_of_commands = 2;





int check_builtin(int count, char** args)
{
  int i;              //incrementor
  int is_command = 0; //checking to see if command is a built in or not

  printf("%i", count);

  if(count > 0)
    {
      for(i=0; i < (number_of_commands); i++)
        {
          is_command = strcmp(commands[i].name, args[0]); //compare strings

          if(is_command == 0)
            {
	      commands[i].func(count, args); //call built in function
              return 0; //it is a command
            }
        }
    }

  return -1; //it is not a command, empty.
}





void do_exit(int count, char** args)
{
  if(count > 2)
    {
      exit(atoi(args[1])); //using user defined exit command
    }
  else
    {
      exit(0); //default exit command is 0
    }
}


void do_aecho(int count, char** args)
{
  int i;          //incrementor
  int do_newline; //whether to add a newline or not
                  // 0 = no new line, -1 = new line

  if(count > 2)
    {
      //check to see if the second argument is a "-n"
      do_newline = strcmp(args[1], "-n");
    }

  if(do_newline == 0) // args[1] is equal to "-n", don't add new ling
    {
      for(i=2; i < (count+1); i++) //i=2 so the commands do not get printed
        { 
          if(args[i]  != NULL) //makes sure the argument isnt null
	  {
          printf("%s", args[i]);
	  }	          
	  if(i < (count))
          printf("%s", " ");
        }     
    }

  if(do_newline != 0) // args[1] isn't equal to "-n" add new line
    {
      for(i=1; i < (count+1); i++) //i=1 so the commands do not get printed
        {
          if(args[i] != NULL) //makes sure the argument isnt null
	  {
          	printf("%s", args[i]);
	  }
          if(i < (count))
          printf("%s", " ");
        }
      printf("%s", "\n");
    }

  return; // nothing after aecho inputed




}

proto (h file)

Code:

/* CS 352 -- Proto Header File 
 *
 *   Author: Cole Markusen
 *   Assignment Number: 2
 *   Class: CSCI 352 -- Unix Developement
 *   Created:  October 5th, 2009 
 *   Modified: October 9th, 2009 
 *
 */

#pragma once

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
void print_array(int count, char** argv, char* line, int pos);
// Function used to parse a line and return the number
// of arguments.
int arg_parse (char *line, char ***argvp);

// Function used to shift the line to the left to remove
// any quote within the line
char* shift(char *line, int length, int i);

// Function used to determine whether the input command
// is a built in or not.
int check_builtin(int count, char** args);

dharmaBum · 10-11-09

One problem I noticed:

You have:

Quote:

int main(void){
...
while(1){
...
processline(line)
...
}
...
}

and

Quote:

void processline(char* line){
...
main();
...
}

I haven't worked out all the logic here you've put here, so I might be missing something.

But there's some recursion going on that can make things messy. Consider:

i.) User does something to go into processline(), and then gets main() called from within processline()
ii.) User repeats above
iii.) User enters in the "break" condition in the main() loop.

The program will not exit here, but will trickle back up through the function calls - i.e., the second nested main() will return back into processline(), which then returns into the first nested main(). The user will need to trigger two more break conditions for the program to exit.

This dovetails nicely into my next concern:

Quote:

return 0;/* Also known as exit (0); */

These are not the same. exit() will entirely stop execution of the program, return simply passes control back to the calling code.

For example, in the above code, using return leads to the messy recursive scheme I described above, while using exit would avoid that altogether by stopping the program the first time it's reached. This, however, has it's own problems, because any program cleanup will not be executed; things like allocated memory not being freed up.

Again, I may just not understand the "big picture" of your code, and this setup may have a purpose I'm not divining. Just giving my first impressions.

deafboy · 10-17-09

Thank you...lol. Oddly enough you pointed out areas that I'm not having a problem with. My issue is coming from my argument parser.

I decided to try and rewrite my parser but I am having a hell of a time clearing my head and coming at it with a new perspective. It's really getting to me. Coding nightmares everynight... blah.

The call to main I admit isn't correct, the other parts you mentioned though are.

Thanks again +rep.

Anyone have some insight on redoing my parser in a new light? lol. I've tried rewriting it half a dozen times but in the end it comes out almost exactly like I have it now. Which doesn't work quite right

help.

serge2k · 4 Weeks Ago

we just had an assignment to write a "shell" in my OS class.

All it has to do it is read the line and execute the process. Used readline, strtok, and (obviously) fork/exec.

you have built something considerably more complex though.

chemicalfan · 4 Weeks Ago

Sounds pretty complex to me - C is scary!!

serge2k · 4 Weeks Ago

asm is scarier.

and scheme will mkae you develop a hatred for brackets.

and prolog will just make your head spin.

deafboy · 4 Weeks Ago

lmao... i've never done asm but scheme is fun. I like it. It's nice once you get the hang of it. Used it last quater in my Automata Theory class.

Prolog is just retarded. lmao.

My third assignment was due friday. Didn't finish and wont be able to turn it in until wednesday for ~75% credit. Each one of these assignments is getting trickier. It's funny though because coming up with the code and writing it doesnt take very long but debugging it and testing it takes forever.

It's fun but at the same time it's a pain rushing to get everything done in a timely manor.

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CS 352 - Unix Software Development

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