Use IO:Handle;

pipe(READFROMCHILD, WRITETOPARENT);
pipe(READFROMPARENT, WRITETOCHILD);

READFROMCHILD->autoflush(1);
READFROMPARENT->autoflush(1);
WRITETOCHILD->autoflush(1);
WRITETOPARENT->autoflush(1);

if ($this = fork) {
   close READFROMPARENT;
   close WRITETOPARENT;
   print WRITETOCHILD "The parent process says hello";
   $thisdata = <READFROMCHILD>;
   print "The parent process read $thisdata";
   close READFROMCHILD;
close WRITETOCHILD;
waitpid(-1, 0);
} else {
   close READFROMCHILD;
close WRITETOCHILD;
   $thisdata = <READFROMPARENT>;
   print "The child process read $thisdata";
   print WRITETOPARENT "The child process says hello";
   close READFROMPARENT;
   close WRITETOPARENT;
   exit;
}