You seem to believe that subs are scoped to the block that contain them. That's not true. Subs are global.

Based on vitoco's example and JadeNB's analysis, I believe that statement should now be considered false. There appears to be two facets of scope that subs demonstrate. On the one hand, no matter where a sub is defined, it can be called anywhere in your program. In that sense, a sub has global scope.

On the other hand, the variables that a sub can see depends on the scope in which the sub is defined. In that sense, a sub has local scope.

Here is a simplified version of vitoco's example:

use strict;
use warnings;
use 5.010;

my $val = 10;

sub f {
    say "in global f, \$val is: $val";
}

f(); #Demonstrates that the global definition of f is overwritten 
     #by the local definition of f (below) at compile time.  As a 
     #result, you won't see output from global f.  When the local f
     #executes instead, the global $val above is hidden by a local
     #$val in the definition of f (below).

say '=' x 20;

sub g {
    my $val = shift;
    say "in g, \$val is: $val";

    #This definition of f closes over $x in previous line.
    sub f {   #line 40
        say "in local f, \$val is: $val";  
    }

    f();
}

g('hello');
say '=' x 20;

g('goodbye');
say '=' x 20;

--output:--
Variable "$val" will not stay shared at 4perl.pl line 41.
Subroutine f redefined at 4perl.pl line 40.
Use of uninitialized value $val in concatenation (.) or string at 4per
+l.pl line 41.
in local f, $val is: 
====================
in g, $val is: hello
in local f, $val is: hello
====================
in g, $val is: goodbye
in local f, $val is: hello
====================
[download]

If a sub truly had global scope, then the local $val would have no affect on the locally defined sub. Instead, the sub would have closed over the global $val, and changes to the local $val would not be seen by the sub.

*Yes, I know that "local $val" and "global $val" are really my variables. However, referring to them as "the my variable $val that was defined in the same block as the nested sub definition" or "the my variable $val declared outside of any blocks" is too unwieldy."

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