in reply to Re: Dynamic "use lib"
in thread Dynamic "use lib"

That won't work. The compile-time effect of 'use' will not be affected by a run-time 'if' block, even if it's inside a BEGIN. You need to wrap it in an 'eval' inside a BEGIN: 

BEGIN {
  if ($version =~ /beta/){
      eval "use lib('/path/to/dev/modules')";
  } else {
      eval "use lib('/path/to/prod/modules')";
  }
}

[download]

Or, simpler, just manipulate @INC directly since that's what 'use lib' is doing: 

BEGIN {
  if ($version =~ /beta/){
      unshift @INC, '/path/to/dev/modules';
  } else {
      unshift @INC, '/path/to/prod/modules';
  }
}

[download]

-sam

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Re: Re: Re: Dynamic "use lib"
by Anonymous Monk on May 21, 2004 at 18:30 UTC
    Actually 'use lib' does a little more than just push into @INC (it also considers architecture specific subdirectories) so you may want to use it after all. 
    BEGIN {
  require lib;
  if ($version =~ /beta/){
      lib->import('/path/to/dev/modules');
  } else {
      lib->import('/path/to/prod/modules');
  }
}

    [download]
[reply]
[d/l]
Re: Re: Re: Dynamic "use lib"
by dragonchild (Archbishop) on May 21, 2004 at 17:26 UTC
    Now, that makes absolutely no sense. BEGIN blocks are supposed to happen AT compile-time, meaning they happen simultaneous with the use statements.

    Or, does each BEGIN-block get its own BEGIN-CHECK-INIT-END sequence?

    ------
    We are the carpenters and bricklayers of the Information Age.

    Then there are Damian modules.... *sigh* ... that's not about being less-lazy -- that's about being on some really good drugs -- you know, there is no spoon. - flyingmoose

    I shouldn't have to say this, but any code, unless otherwise stated, is untested

[reply]
      You're missing the point. The 'use' statement does its thing at compile-time. That means that as soon as Perl compiles a 'use lib' it affects @INC. That's as true inside a BEGIN as it is outside a BEGIN. Here let me demonstrate: 

      BEGIN {
  if (@INC) {
     use lib '/foo';
  } else {
     use lib '/bar';
  }
}
print "INC IS: @INC\n";

      [download]

      Running this code you can see that the 'if' did not effect the 'use' statements. That's because 'if' is a run-time operator and 'use' is a compile-time statement. See: 

      $ perl begin.pl
INC IS: /bar /foo /usr/local/lib/perl5/5.6.1/i686-linux /usr/local/lib
+/perl5/5.6.1 /usr/local/lib/perl5/site_perl/5.6.1/i686-linux /usr/loc
+al/lib/perl5/site_perl/5.6.1 /usr/local/lib/perl5/site_perl .

      [download]

      -sam

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