use Win32::Console qw( CTRL_C_EVENT );

my $pid = open(my $fh_from_child, "$cmd |");

my $output  = '';
while (<$fh_from_child>) { 
   $output .= $_; 
   if ( /waiting for control c/i ) {
      Win32::Console->GenerateCtrlEvent(CTRL_C_EVENT, $pid);
   }
}

close($fh_from_child);