in reply to Problems with 'use lib'

When and where does $projectLocation get defined?

The "use lib" action is done at compile time, before statements like 

  my $projectLocation = '/some/other/place';

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can be executed to set the variable.   You need to force your value to be defined during compilation.   Perhaps this might be more like what you were thinking? 
BEGIN {
  my $projectLocation = '/some/other/place';
  use lib $projectLocation;
}

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But then this gets back to something like the starting question - where does the value for $projectLocation come from?   Ah, an environment variable.   So maybe 
BEGIN {
  use lib $ENV{MYLIBRARYDIR};
  printf "in BEGIN:   '%s'\n", join("', '", @INC );
}

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will do what you want.

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Re: Re: Problems with 'use lib'
by esh (Pilgrim) on Aug 21, 2003 at 07:38 UTC

    I don't think this code will do what you want: 

    BEGIN {
  my $projectLocation = '/some/other/place';
  use lib $projectLocation;
}

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    The "use lib" inside the BEGIN block will be executed before the assignment since it is also inside the BEGIN block. Try this instead: 
    my $projectLocation;
BEGIN {
  $projectLocation = '/some/other/place';
}
use lib $projectLocation;

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    The "use" is like another BEGIN so these two pieces of code will be executed in sequence now.

    -- Eric Hammond

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      I was going to say that wasn't true, but went back and looked at the last test program I was using and decided I hadn't tested that situation correctly.   Using code 
      BEGIN {
    my  $foo = 'foom';
    use lib $foo;
}

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      results in error messages 
      Use of uninitialized value in string eq at /usr/lib/perl5/5.8.0/i386-linux-thread-multi/lib.pm line 29.
Empty compile time value given to use lib at hotshot.pl line 5
      Using your code 
          my  $foo;
BEGIN {  $foo = 'foom'; }
    use lib $foo;
    printf "executing:  '%s'\n", join("', '", @INC );

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      returns the desired results 
      executing:  'foom', '/usr/lib/perl5/5.8.0/i386-linux-thread-multi', ... , '.'
      Just to try something different I tried 
      BEGIN {  our $foo = 'foom';  }
    use lib $foo;

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      which also worked.

      Another thing to put in the list of things to re-study.   Key is that "use" (and other pragmas?) are executed (at compile time) before surrounding code at the same apparent 'level'.   By enclosing code in a BEGIN block ahead of the "use" we force it into compile time execution before the following "use" is executed.   (Or something like that ;-)

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