Thread: Need help please

Hi, i want to make a little command line shell that executes programs with any required arguments.
But i dont understand what is the problem, why the program don´t work.

Code:

main() {
	char cmd[20];
	char s[20];
	int pid,i,status;
	while(1) {
		printf("Console$: ");
		fgets(cmd,sizeof(cmd),stdin);
		for(i=0; i<strlen(cmd); i++) {
			if(cmd[i]!=' ')
				strcpy(s,cmd);
			if(strcmp(s , "exit")==0) {
				printf("Shell Terminate\n");
				break;
			}
		}
		pid = fork();
		if(pid==0)
			execv(s,NULL);
		else
			wait(&status);
	}
}

so how can i make this work:
if i put
>Console$: ls

i want the program execute the ls command and if i put:

>Console$: exit

I quit the program, but it seems he can´t execute any command.

Originally Posted by maritos

so how can i make this work:
if i put
>Console$: ls

i want the program execute the ls command and if i put:

>Console$: exit

I quit the program, but it seems he can´t execute any command.

From your questions, and your code, I'm guessing that you're pretty new to C programming. The reason the "exit" command doesn't work is that you're doing a break from inside a nested loop, and break only takes you out one level. I don't know what you're trying to achieve with the strcpy() in the inner loop, but if you look at the FAQ, check out the man page for the system() library call, and simply walk through your code step-by-step, you'll find that the problem is with your code logic.

Here is a version of your program that I put together in about 5 minutes -- it does what you're looking for.

Code:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
   char cmd[128];       /* a command line buffer */
   int status = 0;      /* return status from system() call */

   while (1)  /* loop until done */
   {
      printf("Console$: ");     /* prompt the user */
      fflush(stdout);           /* display the prompt */
      if (fgets(cmd, sizeof(cmd), stdin) < 0)  /* get a response */
      {  /* read error -- assume end of input */
         printf("Read error on stdin, exiting.\n"); /* print an error */
         break;  /* get out of the loop. */
      }
      if (cmd[strlen(cmd) - 1] < 0x20)  /* trim off a trailing newline */
      {  /* some control character as last character */
         cmd[strlen(cmd) - 1] = '\0'; /* replace it with a nul */
      }
      if (strcmp("exit", cmd) == 0) /* check for "exit" */
      {  /* found the exit string */
         printf("Shell Terminated\n");  /* tell the user */
         break;        /* get out of the loop */
      }
      else
      {  /* Wasn't the exit string */
         printf("About to execute '%s'\n", cmd); /* echo the cmd. */
         status = system(cmd);  /* execute the command */
         if (status != 0)  /* see if there was a problem with the cmd */
         {  /* there was */
            perror(cmd);  /* display an error message */
         }
      }
   }

   exit(0); /* exit the program */
}

I hope this helps. (If I find out that this was for a homework assignment, I'll be somewhat annoyed.)