use warnings;

my $s = "s1";
print "define var: $s\n";
&test;

my $s = "s1-2nd";
print "define var: $s\n";
&test;

sub test{
        print "sub: $s\n";
}

##</code><code>##

"my" variable $s masks earlier declaration in same scope at test.pl line 8.
define var: s1 
Use of uninitialized value $s in concatenation (.) or string at test.pl line 13.
sub:
define var: s1-2nd
sub: s1-2nd

##</code><code>##

use warnings;

my $s = "s1";
print "define var: $s\n";
&test;

sub test{
        print "sub: $s\n";
}

my $s = "s1-2nd";
print "define var: $s\n";
&test;

##</code><code>##

"my" variable $s masks earlier declaration in same scope at test.pl line 12.
define var: s1
sub: s1
define var: s1-2nd
sub: s1

##</code><code>##

define var: s1
sub: s1
define var: s1-2nd
sub: s1-2nd