Thread: simple shell coding

Hi

I need to expand some shell code so it would be able to do more than it is doing now. Currently it can do stuff like quit when q is pressed, display a prompt but not much more. I have to make the shell have capabilities like
cd (changing directories)
redirection of input and output, for example date > storeddate.txt
pipelines, for example ps -ax | grep programname
background processes, for example gcc -c verylargeprogram.c

etc..

this has to be done under a POSIX 1 compliant system.

i have been given the following code:

-----------------------------

Code:

/* 
 * 	simplesh.h
 */

#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/wait.h>
#include <limits.h>

#define  DELIMITERSET " ><|&"

#ifndef  MAX_CANON
 #define MAX_CANON 256
#endif

#define  TRUE 1
#define  FALSE 0
#define  BLANK_STRING " "
#define  PROMPT_STRING "-> "
#define  QUIT_STRING "q"
#define  BACK_STRING "&"
#define  PIPE_STRING "|"
#define  NEWLINE_STRING "\n"
#define  IN_REDIRECT_SYMBOL '<'
#define  OUT_REDIRECT_SYMBOL '>'
#define  NULL_SYMBOL '\0'
#define  PIPE_SYMBOL '|'
#define  BACK_SYMBOL '&'
#define  NEWLINE_SYMBOL '\n'

int      makeargarray (char *s, char *delimiters, char ***argvp);
int      parsefile (char *inbuf, char delimiter, char **v);
int      redirect (char *infilename, char *outfilename);
void     executecmdline (char *cmd);
int      connectpipeline (char *cmd, int frontfd[], int backfd[]);

-----------------------------------------------------------------------

/* makeargarray.c */

#include "simplesh.h"

/* Make arg array (*arvp) for tokens in s which are separated by
 * delimiters. Return -1 on error, or the number of tokens otherwise.
 */

int
makeargv (char *s, char *delimiters, char ***argvp)
{
    char *t;
    char *snew;
    int   numtokens;
    int   i;

  /* snew is the start of string after skipping leading delimiters */
    snew = s + strspn (s, delimiters);

    /* Create space for a copy of snew in t */
    if ((t = calloc(strlen(snew) + 1, sizeof(char))) == NULL)
    {
        *argvp = NULL;
         numtokens = -1;
    }    
    else  /* count the number of tokens in snew */
    {
        strcpy (t, snew);
        if (strtok(t, delimiters) == NULL)
            numtokens = 0;
        else
            for (numtokens=1; strtok(NULL,delimiters) != NULL; numtokens++)
            ;
        /* create an argument array to contain pointers to tokens */
        if ((*argvp = calloc(numtokens + 1, sizeof(char *))) == NULL)
        {
            free (t);
            numtokens = -1;
        }
        else /* insert pointers to tokens into the array */
        {
            if (numtokens > 0)
            {
                strcpy (t, snew);
                **argvp = strtok (t, delimiters);
                for (i = 1; i < numtokens + 1; i++)
                    *((*argvp) + i) = strtok (NULL, delimiters);
            }
            else
            {
                **argvp = NULL;
                free (t);
            }
        }
    }
    return numtokens;
}


--------------------------------------------------------------------------------


/*
 * 	simplesh2.c
 *
 * 	A simple shell - second attempt
 */

#include "simplesh.h"

int
main (void)
{
    char inbuff[MAX_CANON+1];
    pid_t child_pid;


    while (1)
    {
        fputs (PROMPT_STRING, stdout);
        if (fgets(inbuff, MAX_CANON, stdin) == NULL)
            break;

        if (*(inbuff + strlen(inbuff) - 1) == NEWLINE_SYMBOL)
            *(inbuff + strlen(inbuff) - 1) = 0;

        if (strcmp(inbuff, QUIT_STRING) == 0)
            break;
        else
        {
            if ((child_pid = fork()) == 0)
            {
                char **chargv;

                if (makeargv(inbuff, BLANK_STRING, &chargv) > 0)
                {
                    if (execvp(chargv[0], chargv) == -1)
                    {
                        perror ("Invalid command");
                        exit (1);
                    }
                }
                exit (1);    
            }
            else if (child_pid > 0)
                wait (NULL);
        }
    }
    return 0;
}

-------------------------------------------------------------------




how do i do this? where do i find info on this sort of stuff?

thanx everyone

I don't know if this will help you too much but as far as I know, the shell is the user interface to the operating system. I believe that a shell performs a great deal of system calls, so definately research system calls and use them extensively in your shell.

k sorry bout that code thing - ill try to use the tags fro now on.
i have more questions.
i need to get the bit of code after the fork() call to go into a different file called executecmdline. this is sorf of aranged for in the .h file.
so i've been trying to get this bit (more or less):

Code:

char **chargv;

                if (makeargv(inbuff, BLANK_STRING, &chargv) > 0)
                {
                    if (execvp(chargv[0], chargv) == -1)
                    {
                        perror ("Invalid command");
                        exit (1);
                    }
                }
                exit (1);

into that void executecmdline (char *cmd) c file but it dont wanna compile. ive been trying to change the various variables and play with that pointer stuff but i dont know much about low level c prog. any help?

anyone?