cis-lclient06:~/class/nov22>more exec9.c
#include <syscall.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#define SIZE 40
int main(void) {
    char buf[SIZE+1], argv0[SIZE], argv1[SIZE], argv2[SIZE]; 
    int argc, pid;
    while (1) {
       pid = fork();
       if (pid == 0) {
          printf("\nbsh->");
          if (gets(buf) == (char *) NULL) exit(1); /* GETS IS UNSAFE */
          argv0[0] = '\0';
          argc = sscanf(buf, "%s %s %s", argv0, argv1, argv2);
          switch (argc) {
             case 1:
                execlp(argv0, argv0, (char *) NULL); 
                break;
             case 2:
                execlp(argv0, argv0, argv1, (char *) NULL); 
                break;
             case 3:
                execlp(argv0, argv0, argv1, argv2, (char *) NULL); 
                break;
         }
         printf("%s: command not found\n", argv0);
         return;
      } else {
         wait();
      }
   }
}
cis-lclient06:~/class/nov22>gcc exec9.c
/tmp/cc0YvKHJ.o: In function `main':
exec9.c:(.text+0x3e): warning: the `gets' function is dangerous and should not be used.
cis-lclient06:~/class/nov22>./a.out
bsh->nano new.c
#include <stdio.h>
main() {
   printf("How do you like Bob's shell?\n");
}
^X
Save modified buffer (ANSWERING "No" WILL DESTROY CHANGES) ?  Y
File Name to Write: new.c  
bsh->gcc new.c
bsh->./a.out
How do you like Bob's shell?
bsh->^C
cis-lclient06:~/class/nov22>