Maybe now is a good moment to step back and explain in plain English what you want the script to do.

From your various replies, it seems to me that you want your script to read from STDIN if there is input piped to it, but not read from STDIN when it is launched interactively.

The easy approach would be to use the -t test (or even better, -p) to check whether STDIN is connected to an interactive terminal or not.

In your commented reference to 1175906, you erroneously state that there was a change in 5.22 in the handling of @ARGV resp. while( <> ), but the comments there state that no such change happened between 5.002 and 5.24. You might want to revisit that node and maybe update your comment accordingly.