The reason why you get the message is because $var is not defined in test.pl, so you need to explicitly tell Perl which module (package) you want it to look in for $var. The program will work if you define testlib.pl as:

package testlib;
our $var = "Lord only knows if this will work...";
1;
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and change the print statement in test.pl to: print $testlib::var;

Now, if you want to do things the recommended way by using a proper module you can do it like this:

# testlib.pm
package testlib;

use strict;
our @EXPORT = qw( $var ); #place all the variables you want to export 
+by default in here (c.f. @EXPORT_OK)
use Exporter;
our @ISA = qw(Exporter);

our $var = "Lord only knows if this will work...";
1;
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#!/usr/bin/perl -w
# test.pl
use strict;
use CGI::Carp qw(fatalsToBrowser warningsToBrowser);
use CGI ':standard';

use testlib; # will automagically import $var into current namespace

print "Content-type: text/html\n\n";
print $var;

exit;
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-imran