Implementing a simple shell

Question 1

First of all, your fgets is reading to a single character buff. You should read into a buffer of characters. Second, fgets keeps the newline at the end of the read string, so you may want to remove it first, e.g.:

char buff[4096];
if (!fgets(buff, sizeof(buff), stdin)) {
    // error or EOF
    return 1;
}
int len = strlen(buff);
if (len > 0 && buff[len-1] == '\n') {
    buff[--len] = '\0';
}
char *whtspc = strtok(buff, " ");

You must also replace all references to &buff with buff.

In addition to this, your malloc is also wrong, and allocates one character less than is required (strlen is without the terminating NUL):

if (!(comand[i] = malloc(strlen(whtspc)+1))) {
    return 1; // out of memory
}
(void) strcpy(comand[i], whtspc);

Correspondingly your strncpy was copying one character less than required. This is what made your original code accidentally work for a single-word input because it had the effect of removing the trailing '\n' for you in that case, but in every other case it removed the last character of the word itself.

And the second argument to execvp should be just the comand (sic) array:

execvp(comand[0], comand);

Question 2

The first argument to fgets should be a pointer to a buffer where the string is copied into. You are passing a pointer to a single char.

Second, execvp expects two arguments: a filename and a null-terminated list of command-line arguments which, by convention, starts with the filename itself.

I took the liberty to make some modifications to your code, both fixing the issues I pointed above and making it a little more readable.

Note that there's a memory leak in the code below (fix it :). There might be other issues that I didn't notice.

I implemented a shell a while ago; if you want to take a look, my GitHub URL is in my profile (BEWARE: ugly college homework code).

Hope it helps!

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

#define COMLEN 4096                                                                                     
#define COMARG_N 32                                                                                     
#define TRUE 1

int main(int argc, char *argv[]) 
{                                                                                                       
    char *token;                                                                                        
    char *args[COMARG_N];                                                                               
    char *buff;                                                                                         
    int i;                                                                                              
    pid_t pid;                                                                                          

    while(TRUE) {                                                                                       
        printf("simsh: ");                                                                            

        buff = (char*) malloc(sizeof(char) * COMLEN);                                                 
        fgets(buff, COMLEN, stdin);                                                                   

        if (buff[strlen(buff) - 1] == '\n')                                                           
            buff[strlen(buff) - 1] = '\0';                                                            

        i = 0;                                                                                        
        token = strtok (buff, " ");                                                                   

        while (token != NULL && i < COMARG_N - 1) {                                                   
            args[i] = token;                                                                          
            token = strtok (NULL, " ");                                                               
            i++;                                                                                      
        }                                                                                             

        args[i] = NULL;                                                                               

        pid = fork();                                                                                 
        if (pid == 0)                                                                                 
            execvp(args[0], &args[0]);                                                                
        else                                                                                          
            waitpid(pid, &i, WUNTRACED | WCONTINUED);                                                 

        free(buff);                                                                                   
    }                                                                                                 

    return 0;                                                                                             
}