Lexical scoping is your friend:

I think this will demonstrate what you're looking for?

#!/usr/bin/perl

use strict;

my $tossMeAbout = 'Initial value';

{
    my $updatedValue = &adjustValue($tossMeAbout);
    print "-----------------------------------------------------------
+--------------------\n";
    print "    MAIN:       \$tossMeAbout = [$tossMeAbout]\n";
    print "    MAIN:      \$updatedValue = [$updatedValue]\n";

    my $additionalValue = &adjustValue($updatedValue);
    print "-----------------------------------------------------------
+--------------------\n";
    print "    MAIN:       \$tossMeAbout = [$tossMeAbout]\n";
    print "    MAIN:      \$updatedValue = [$updatedValue]\n";
    print "    MAIN:   \$additionalValue = [$additionalValue]\n";

    print "-----------------------------------------------------------
+--------------------\n";
}

exit;

{
    my $persistentValue;

    sub adjustValue
    {
        my ($requestedValue, @garbage) = @_;
        if (!defined $requestedValue) { $requestedValue = ''; }

        my $returnValue = '';

        print "-------------------------------------------------------
+------------------------\n";
        print "SUB BEGIN:   \$requestedValue = [$requestedValue]\n";
        print "SUB BEGIN:  \$persistentValue = [$persistentValue]\n";
        print "SUB BEGIN:      \$returnValue = [$returnValue]\n";

        # Append requested value to persistent value
        if (!defined $persistentValue)
        {
            $persistentValue = $requestedValue;
        }
        else
        {
            $persistentValue .= "/$requestedValue";
        }

        $returnValue = "<$requestedValue>";

        print "-------------------------------------------------------
+------------------------\n";
        print "  SUB END:   \$requestedValue = [$requestedValue]\n";
        print "  SUB END:  \$persistentValue = [$persistentValue]\n";
        print "  SUB END:      \$returnValue = [$returnValue]\n";

        return $returnValue;
    }
}

__END__
[download]

Results:

C:\Steve\Dev\PerlMonks\P-2015-03-19@1121-Durable-Subroutine-Data>persi
+stent1.pl
----------------------------------------------------------------------
+---------
SUB BEGIN:   $requestedValue = [Initial value]
SUB BEGIN:  $persistentValue = []
SUB BEGIN:      $returnValue = []
----------------------------------------------------------------------
+---------
  SUB END:   $requestedValue = [Initial value]
  SUB END:  $persistentValue = [Initial value]
  SUB END:      $returnValue = [<Initial value>]
----------------------------------------------------------------------
+---------
     MAIN:       $tossMeAbout = [Initial value]
     MAIN:      $updatedValue = [<Initial value>]
----------------------------------------------------------------------
+---------
SUB BEGIN:   $requestedValue = [<Initial value>]
SUB BEGIN:  $persistentValue = [Initial value]
SUB BEGIN:      $returnValue = []
----------------------------------------------------------------------
+---------
  SUB END:   $requestedValue = [<Initial value>]
  SUB END:  $persistentValue = [Initial value/<Initial value>]
  SUB END:      $returnValue = [<<Initial value>>]
----------------------------------------------------------------------
+---------
     MAIN:       $tossMeAbout = [Initial value]
     MAIN:      $updatedValue = [<Initial value>]
     MAIN:   $additionalValue = [<<Initial value>>]
----------------------------------------------------------------------
+---------
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.