create and open file "myfile.txt"
writeline "0" to "myfile.txt"
writeline "1" to "myfile.txt"
create child
...

Get 2 lines from myfile.txt
Use child   (But how?)
Calculate fibonacci
Write the result to myfile.txt

#! /bin/bash

fork() ## Fibonacci Object Reader and Kalculator
{
    set -- $( < "$fibfile" )
    shift "$(( $# - 2 ))"
    fibnum=$(( $1 + $2 ))
    printf "%d\n" "$fibnum" >> "$fibfile"
}

usage()
{
    printf "USAGE: %s FILE NUM\n" "${0##*/}"
}

[ $# -lt 2 ] && { usage >&2; exit 1; }

fibfile=$1
desired=$2
fibnum=1
printf "%s\n" 0 1 > "$fibfile"

while [ $fibnum -lt $desired ]
do
  fork
done

#include <unistd.h>
int main(int argc, char *argv[]){
   int pid;

   printf("Only one process\n");
   pid = fork();

   // right now, there (probably) is 2 processes executing this same code.
   if(pid == -1){
      perror("impossible to fork");
      exit(1);
   }

   // we KNOW now there are 2 processes executing the following if statement.

   if(pid > 0) // anything inside this block will ONLY be executed by the PARENT process.
      printf("I am the parent, pid=%d\n", getpid());
   else
      if(pid == 0) // anything inside this block will ONLY be executed by the CHILD process.
         printf("I am the child, pid=%d\n", getpid());

   // BOTH processes will execute everything else
   exit(0);
}