G'day pritesh,

It seems the answers you've already received cover what you're asking. However, I felt it was important to advise that this is a situation you should avoid in the first place.

Variables with file scope, regardless of whether they're lexical or dynamic, suffer all the same classic problems as global variables: action at a distance; unclear logic; hard to debug; problematic refactoring; and so on.

In the following demonstration script, I've reproduced all of the types of actions you're attempting, without any variables with file scope. Things to note in particular:

• $val is declared in three separate places. Each declaration is within its own, limited scope. None of the $val variables have any relationship to any of the other $val variables.
• &show_value is a read-only operation: it receives its data as a value. &change_value is a read-write operation: it receives its data as a reference. &unrelated_value uses its own internal, lexically isolated, data: it's called without arguments.
• &show_value and &change_value are abstracted such that they have no dependencies on external data. They could easily be refactored into their own module.
• &show_value is called from the main (anonymous block) code, from within &change_value, and indirectly from &unrelated_value (via &change_value). &change_value is called from the main (anonymous block) code and from &unrelated_value.

Here's the code:

#!/usr/bin/env perl -l

use strict;
use warnings;

{
    my $val = 10;

    print "INIT: $val";
    show_value($val);
    change_value(\$val, 200);
    show_value($val);
    unrelated_value();
    show_value($val);
    print "LAST: $val";
}

sub show_value {
    my ($val) = @_;

    print '* Show Value';
    print "Value: $val";

    return;
}

sub change_value {
    my ($val_ref, $new_value) = @_;

    print "* Change Value: $$val_ref to $new_value";
    show_value($$val_ref);
    $$val_ref = $new_value;
    show_value($$val_ref);

    return;
}

sub unrelated_value {
    my $val = 42;

    print '* Unrelated Value';
    change_value(\$val, 999);

    return;
}
[download]

Output:

INIT: 10
* Show Value
Value: 10
* Change Value: 10 to 200
* Show Value
Value: 10
* Show Value
Value: 200
* Show Value
Value: 200
* Unrelated Value
* Change Value: 42 to 999
* Show Value
Value: 42
* Show Value
Value: 999
* Show Value
Value: 200
LAST: 200
[download]

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