package MyPack;
my $a;
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Using 'our' makes the variable known at the global scope level (that is, everyone can access it now):

package MyPack;
our $a;
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So 'our' can be considered to be declaring which variables are public in a object-oriented sense. It mostly replaces the functionality of Exporter which can be awkward to use.

You can replace our with use vars.

My program tempo2.pl is as follows:

use strict;
use MyPack;
my $myString = $MyPack::a;
print $myString;
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My module MyPack.pm can be either:

package MyPack;
require Exporter;
$a = "Read from Mypack"
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or

package MyPack;
our $a = "Read from Mypack"
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The program tempo2.pl runs properly regardless of whether I use Exporter or 'our'. So my question is, when would one prefer the use of 'our' instead of Exporter?

Is the use of 'our' in order to avoid possibly polluting a namespace by exporting all of the package variables?

Yes, that's one considered use. If you know C++ or Java, then by using Exporter without restrictions, you may all your variables of your package public; this is usually not good OO programming practice. Using our specifies only which variables you want public, which is the better way to go.

Also, to note: you should have "my $a = ..." in the Exporter example to keep everything strict.

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Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain