Conditional 'use lib'

bjdean has asked for the wisdom of the Perl Monks concerning the following question:

Greetings folks,

I've recently come across a problem whereby I'd like to conditionally use 'use lib' (which doesn't work due to the early order of processing 'use' in compilation).

The question then, is there a better way then this:

BEGIN {
    use Sys::Hostname;
    if ( hostname() eq 'foo.bar.org' ) {
        unshift @INC, ('/alternate/libdir');
    } else {
        unshift @INC, ('/default/libdir');
    }
}

To achieve something close to to 'meaning' of:

BEGIN {
    use Sys::Hostname;
    if ( hostname() eq 'foo1.bar.org' ) {
        use lib '/alternate/libdir';
    } else {
        use lib '/default/libdir';
    }
}

Comment on Conditional 'use lib'

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Re: Conditional 'use lib'
by Chmrr (Vicar) on Feb 26, 2003 at 08:04 UTC

The work is done inside of lib.pm's import method, so you might try:

BEGIN {
  use Sys::Hostname;
  require lib;
  if (hostname() eq 'foo.bar.org') {
    lib->import('/alternate/libdir');
  } else {
    lib->import('/default/libdir');
  }
}
[download]

The advantage of this over the unshift trick is that you'll get architecture-dependent paths added, as well.

perl -pe '"I lo*`+$^X$\"$]!$/"=~m%(.*)%s;$_=$1;y^`+*^e v^#$&V"+@( NO CARRIER'

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Re^2: Conditional 'use lib'

by Anonymous Monk on Dec 04, 2007 at 18:48 UTC

Just found an even easier way, which seems to work for me: my $module = "ROX::Filer"; eval "use $module"; die "couldn't load $module : $!n" if ($@); See http://weierophinney.net/matthew/archives/23-conditional-use-in-perl.html

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Re: Conditional 'use lib'
by Abigail-II (Bishop) on Feb 26, 2003 at 08:00 UTC

if

    use if hostname eq 'foo1.bar.org', lib => '/alternate/libdir';
    use if hostname ne 'foo1.bar.org', lib => '/default/libdir';
[download]

Abigail

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Re: Conditional 'use lib'
by PodMaster (Abbot) on Feb 26, 2003 at 08:03 UTC

use

use lib ( 1 ? 'foo' : 'bar' );
die @INC;
[download]

use

import

MJD says you can't just make shit up and expect the computer to know what you mean, retardo!
I run a Win32 PPM repository for perl 5.6x+5.8x. I take requests.
** The Third rule of perl club is a statement of fact: pod is sexy.

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Re: Conditional 'use lib'
by dbp (Pilgrim) on Feb 26, 2003 at 08:11 UTC

If you look at the perldoc for lib you'll see that all it does besides unshift the path into @INC is add architechture specific directories if it finds them and remove trailing duplicates from @INC. A quick look at the lib module's source should give you an idea of how to proceed.

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