Diddling @INC, order of entries in it

David Cantrell david at cantrell.org.uk
Wed Aug 1 17:24:11 BST 2007

[ Adriano Ferreira CCed so he knows just what kind of insanity I'm
  inflicting on his code :-) ]

I'm hacking around in the guts of Devel::Hide, trying to add a facility
to make it hide modules from child processes created by fork-and-exec,
so eg ...

    use Devel::Hide qw(-fromchildren Foo::Bar);

    system("perl -MFoo::Bar ..."); # Foo::Bar is unavailable here

D::H works by putting a coderef into @INC, which checks what you're
trying to load, and which fails as appropriate.

I have it so that if you pass the magic value '-fromchildren' to D::H's
import() like above, it puts MDevel::Hide=Foo::Bar into PERL5OPT.  And it

It works right up until the child process does this ...

    use lib 'my/secret/stash/of/modules';
    use Foo::Bar;

cos then, 'my/secret/stash/of/modules' gets stuffed into @INC *before*
the coderef, and so if Foo::Bar can be found under there, it gets
loaded.  I don't want this to happen, partly because it makes writing
the tests (which start with 'use lib "t"') for the new bits of code in
Devel::Hide a bit annoying.

Can anyone think of a nifty way around this?  The only one I can think
of is to have Devel::Hide mess around in the guts of lib.pm and change
them so that the reference to Devel::Hide's magic subroutine *always*
comes first.

If I *do* have to mess around in lib's guts, I imagine what I want to
do is replace its import() with one that goes ...

sub import {
    # call the original import(), save its return value
    search @INC and move my magic subroutine to the beginning
    # return the original import()'s return value

And indeed *should* I be trying to subvert 'use lib' like this?  I can
make the tests pass by putting Mlib=t in the right place in PERL5OPT, of
course, so perhaps that's the better choice.

David Cantrell | Reality Engineer, Ministry of Information

I hate baby seals.  They get asked to all the best clubs.

More information about the london.pm mailing list