Variable protection

I read somewhere that you can/should protect variables from being accessed outside of scope.  say I have the following code.
#!/opt/perl/bin/perl -w

$scriptname = $0;
$scriptname =~ s/.*\///;

use FileHandle;
require "/home/oliver/perl/dev/lib.pm";

umask 0;
&init_logfile;
&current_logfile_name;
$logfile_name = "Death_to_Sanity";
print "$logfile_name\n";
&current_logfile_name;


-------library.pm----------
sub init_logfile {
    $logfile_name = $scriptname . "." . $$ . ".log";

    local $ret_val;
    $ret_val = sysopen(ERROR_LOG, $logfile_name, O_WRONLY|O_CREAT, 0666);
    if ( $ret_val ) {
        varify_variable( "Start Time: `date` ", $debug );
    } else {
        die("Can't open Log file $logfile_name !");
    }
}

sub varify_variable {
    local $test_string = shift;
    local $log_level = shift;

    print ERROR_LOG "$test_string\n";
    print "$test_string\n" if $log_level;
}
sub current_logfile_name {
    print STDERR "Current Value $logfile_name\n";
}
1;


------OutPut------
example
Current Value example.5923.log
Death_to_Sanity
Current Value Death_to_Sanity
 
------Desired result------

What I would like to happen is either the $logfile_name variable to be local to the "lib.pm" file and only be modifiable by functions of that lib or to have an error kick off if the value has been changed.
SafeSqlAsked:
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rj2Connect With a Mentor Commented:
my $logfile_name;
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SafeSqlAuthor Commented:
That means that the developer would have to know that they can't declare the variable global.  If they stomp on one of my variables the script could be in trouble.  I want the pm file variables to be called but separated from the calling script. see the difference?  If I put the my in the .pm file it is lost after the call is finished.

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rj2Commented:
use my, but move the declarion to the top of library.pm
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inq123Commented:
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:

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