problem with fork()

Posted by john on Stack Overflow See other posts from Stack Overflow or by john
Published on 2010-06-15T05:27:37Z Indexed on 2010/06/15 5:32 UTC
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I'm writing a shell which forks, with the parent reading the input and the child process parsing and executing it with execvp.

pseudocode of main method:

do{
 pid = fork();
 print pid;
 if (p<0) { error; exit; }
 if (p>0) { wait for child to finish; read input; }
 else { call function to parse input; exit; }
}while condition
return;

what happens is that i never seem to enter the child process (pid printed is always positive, i never enter the else). however, if i don't call the parse function and just have else exit, i do correctly enter parent and child alternatingly.

full code:
int main(int argc, char *argv[]){

 char input[500];
 pid_t p;
 int firstrun = 1;

 do{

  p = fork();

  printf("PID: %d", p);

  if (p < 0) {printf("Error forking"); exit(-1);}

  if (p > 0){

   wait(NULL);
   firstrun = 0;
   printf("\n> ");
   bzero(input, 500);
   fflush(stdout);
   read(0, input, 499);
   input[strlen(input)-1] = '\0';

  }

  else exit(0);

  else { if (parse(input) != 0 && firstrun != 1) { printf("Error parsing"); exit(-1); } exit(0); }

 }while(strcmp(input, "exit") != 0);

 return 0;
}

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