#!perl
use v5.10;
use strict;
use warnings;

my $a = shift;

sub f {
  say "global f";
}

sub g {
  say "global g";
  my ($a) = @_;
  sub f {
    say "local f ($a)"; # line 16
  }
  f();
}

f();
g(shift);
f();

__END__

C:\Temp>localsub.pl
Variable "$a" will not stay shared at C:\Temp\localsub.pl line 16.
Subroutine f redefined at C:\Temp\localsub.pl line 15.
Use of uninitialized value $a in concatenation (.) or string at C:\Temp\localsub.pl line 16.
local f ()
global g
Use of uninitialized value $a in concatenation (.) or string at C:\Temp\localsub.pl line 16.
local f ()
Use of uninitialized value $a in concatenation (.) or string at C:\Temp\localsub.pl line 16.
local f ()

C:\Temp>localsub.pl AAA BBB
Variable "$a" will not stay shared at C:\Temp\localsub.pl line 16.
Subroutine f redefined at C:\Temp\localsub.pl line 15.
Use of uninitialized value $a in concatenation (.) or string at C:\Temp\localsub.pl line 16.
local f ()
global g
local f (BBB)
local f (BBB)