accessing variables in subroutines using perl

Question

The following example doesn't compile:

use strict;
use warnings;

sub test {
 print $counter . "n";
}

my $counter = 0;
while($counter < 5) {
 test();
 $counter++;
}

It says "Global symbol "$counter" requires explicit package name ...". When I put the subroutine after the 'while' loop, it works just fine, so what's the problem?

Answer 1

The subroutine does not see the lexical $counter variable because it was declared after its scope. For more information, see:
http://www.plover.com/FAQs/Namespaces.html

Answer 2

You trying to print a variable $counter that was initialized outsider the scope of the subroutine.