Constants imported from other perl scripts doesn't want to exist :(

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

I am trying to make a configuration file which another perl script reads. Looking at other peoples scripts they all use require() and wrap it in a BEGIN block which works fine but not in this case since I am using $dir in the filename and $dir is dependent on %ENV which isn't known at compile time I guess. What I get is a "Undefined subroutine" error. Something I don't understand, why would it even matter if it's in a BEGIN block? The require()'s come before the usage of those constants anyway so it shouldn't matter?

Example:

#config.pl
use strict;

eval 'use constant SOMETHING => "asdf"' unless(defined(\&SOMETHING));

1;

#test.pl
use strict;
use File::Basename;

my $dir = dirname($ENV{"SCRIPT_FILENAME"})."/";
require("${dir}config.pl");

print &SOMETHING;
[download]

Comment on Constants imported from other perl scripts doesn't want to exist :( Download Code

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Re: Constants imported from other perl scripts doesn't want to exist :( by Errto (Vicar) on Sep 17, 2005 at 18:52 UTC
The problem is actually in your `unless` clause. According to the docs for defined, the way to tell if a subroutine is defined is to simply call `defined(&SOMETHING)`. Putting the backslash in front of it will actually cause it to return a valid (non-undef) reference value, albeit to an undefined subroutine.	[reply] [d/l] [select]
Re: Constants imported from other perl scripts doesn't want to exist :( by borisz (Canon) on Sep 17, 2005 at 18:54 UTC
The problem is you test `unless(defined (\&SOMETHING));` but you want `unless ( defined(&SOMETHING));`. Boris	[reply] [d/l] [select]
Re^2: Constants imported from other perl scripts doesn't want to exist :( by OnionKnight (Sexton) on Sep 17, 2005 at 19:01 UTC
I changed it but it didn't make any difference.	[reply]
Re^3: Constants imported from other perl scripts doesn't want to exist :( by borisz (Canon) on Sep 17, 2005 at 19:05 UTC
I'm sure, you have a typo somewhere. This should work. `use strict; eval 'use constant SOMETHING => "asdf"' unless(defined(&SOMETHING)); 1;` [download] Boris	[reply] [d/l]
Re^4: Constants imported from other perl scripts doesn't want to exist :( by OnionKnight (Sexton) on Sep 17, 2005 at 19:40 UTC
Re^5: Constants imported from other perl scripts doesn't want to exist :( by borisz (Canon) on Sep 17, 2005 at 20:48 UTC
mod_perl and BEGIN blocks by rruiz (Monk) on Sep 18, 2005 at 10:37 UTC
Re: Constants imported from other perl scripts doesn't want to exist :( by shady (Sexton) on Sep 17, 2005 at 19:04 UTC
I suggest you make configuration module config.pm and to declare standart interface for it. Then you may to define all config parameters inside this module and export it. For example: `package config; use strict; use Exporter; our (@ISA, @EXPORT, @EXPORT_OK); @ISA = qw(Exporter); @EXPORT = qw($param_1, $param_2, $param_3); our $param_1 = 'foo'; our $param_2 = 'bar'; ... 1;` [download]	[reply] [d/l]
Re: Constants imported from other perl scripts doesn't want to exist :( by phaylon (Curate) on Sep 17, 2005 at 18:51 UTC
Well, `BEGIN { if ( $ENV{TEST} ) { use constant FOOBAR => 23, } } print 'Foobar: ', FOOBAR, "\n";` [download] works just fine, if it's that what you're looking for. Ordinary morality is for ordinary people. -- Aleister Crowley	[reply] [d/l]