in reply to passing $_ to my function

You could try using the & form of a subroutine call: 
for (keys %online_users) {
 if (policy_is_expired($_)) {
  &logoff_user;
 }
}

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This form passes @_ to the sub if no arguments are given.

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Re^2: passing $_ to my function
by Aristotle (Chancellor) on Sep 30, 2002 at 13:03 UTC
    No, that won't work. You're passing @_, which is not the same as $_.

    Makeshifts last the longest.

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