Something silly...

You can use tie to follow your variable use during the run of your program.

Keep in mind that you can't directly access the name of the variable yourself, you have to pass the name as a parameter to your bound object.

The code would go like this:

Package Defined (Defined.PM)

package Defined;

use strict;
use warnings;

sub TIESCALAR { 
    my $class = shift;
    my $name = shift;
    my $self = { 'NAME' => $name,
             'DEFINED' => undef, };
    return bless ($self, $class);
}

sub FETCH {
    my $self = shift; 
    my $name = $self->{'NAME'}; 
    my @caller = caller; 
    if (defined $self->{'DEFINED'}) {
           print STDERR "@caller -> $name defined\n";
        } else {
         print STDERR "@caller -> $name undefined\n";
    }        
}

sub STORE {
    my $self = shift;
    my $value = shift;
    my $name = $self->{'NAME'};
    my @caller = caller;
    $self->{'DEFINED'} = $value;
    print STDERR "@caller -> $name defined with value $value\n";
}

1;
[download]

The caller (test.pl)

#!/usr/bin/perl

use Defined;

use strict;
use warnings;

my $var;
tie $var, 'Defined', '$var';

print $var;
$var = 1;
print $var;
$var = 5
[download]

Output

bash-3.00$ ./test.pl
main ./test.pl 11 -> $var undefined
main ./test.pl 12 -> $var defined with value 1
main ./test.pl 13 -> $var defined
main ./test.pl 14 -> $var defined with value 5
[download]

As I said, a bit silly. However, it might helpt in some cases of debugging.

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