#!/usr/bin/perl

BEGIN {
    *CORE::GLOBAL::getppid = sub () {
        return "Hello world!\n" . CORE::getppid();
    }
}

print getppid();

##</code><code>##

*CORE::GLOBAL::getppid = sub () {
    return "Hello world!\n" . CORE::getppid();
};
1;

##</code><code>##

$ perl -Mmygetppid -e "print getppid()"
Hello world!
23726