I've been asked recently how to tell which perl module overrides a function. Here's an exapmle I managed to write. It's incomplete and most certainly buggy, but I don't think the task in question is worth a full-blown CPAN module anyway.
#!/usr/bin/perl -w

use strict;

BEGIN {
use Guard;
use Carp;
{
  my $guard = guard { Carp::cluck "Function replaced!" };
  my $code = \&time;
  *time = sub { return $code->(@_); undef $guard; };
};
};

BEGIN { print time(), "\n"; };

use Time::HiRes qw(time);

print time, "\n";
I welcome critique on this one.

In reply to Find out who redefined a subroutine by Dallaylaen

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