Update: I assuming from your typically terse description that you goal is to override the function of the built-in select only within the IO::Select module without overriding the select method it presents to its callers.

If that is not the case, perhaps you could clarify your requirements?

Yes. "CORE::GLOBAL::" is too aggressive.

Hm. The CORE::GLOBAL discussion is only a one part of the discussion referenced.

There is also use REGlob 'glob';            # override glob() in Foo:: only, amongst others.

But, to answer your specific problem, I'd suggest adding:

sub yourSelect {
    ...
}

sub select {
   local *CORE::GLOBAL::select = *yourSelect;
  shift
    if defined $_[0] && !ref($_[0]);

  my($r,$w,$e,$t) = @_;
  my @result = ();

  my $rb = defined $r ? $r->[VEC_BITS] : undef;
  my $wb = defined $w ? $w->[VEC_BITS] : undef;
  my $eb = defined $e ? $e->[VEC_BITS] : undef;

  if(select($rb,$wb,$eb,$t) > 0)
 ################################################
}
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Wherever select is used in IO::Select. Make it conditional if appropriate.