Lets examine a quick example:

#!/usr/bin/perl
use strict;
use warnings;

use vars qw(%hash);

sub foo {
   $hash{$_[0]}+=3;
}

sub bar {
   $hash{$_[0]}++;
   foo($_[0]);
}

foreach my $i (0..10) {
   my %hash;

   $hash{$i} = $i*3;
   bar($i);
   foo($i);

   foreach my $j (sort keys %hash) {
      print "hash{$j} = $hash{$j}\n";
   }
}
print "done\n";

foreach my $j (sort keys %hash) {
   print "hash{$j} = $hash{$j}\n";
}
[download]

Oh, and each time through we should end up with a new empty hash too, so if we see repeaters, then the hash is sticking around

Run the code and we get this output:

hash{0} = 0
hash{1} = 3
hash{2} = 6
hash{3} = 9
hash{4} = 12
hash{5} = 15
hash{6} = 18
hash{7} = 21
hash{8} = 24
hash{9} = 27
hash{10} = 30
done
hash{0} = 7
hash{1} = 7
hash{10} = 7
hash{2} = 7
hash{3} = 7
hash{4} = 7
hash{5} = 7
hash{6} = 7
hash{7} = 7
hash{8} = 7
hash{9} = 7
[download]

Scoping is causing issues for you. Neither foo() nor bar() know anything about the private %hash we created by the "my %hash;" line within the foreach loop. bar() is creating a new global version of that hash and hash entry when you call it, and foo() is likewise acting on that new global version of %hash. That is why the initially printed values are only multiplied by three and the remaining global %hash all have values of 7 once you're out of the foreach loop .

So, how do you fix the problem? Either don't use "my %hash;", and continue to use a global %hash variable (not really recommended, but it works) or start passing a reference to the hash to the subroutines that need to access it. If you don't use "my %hash", then the "undef %hash;" line will be needed at the end of your foreach loop.

Update: You can't use a "my %hash" in this case, as you can't take a reference to a my variable (at least I'm pretty sure you can't) since it doesn't exist on the glob table like a normal variable does. Just add the "undef %hash;" at the end of the foreach loop and it should start working more correctly than it currently does.

-Scott

Update: Fixed various typo's... Update 2: Made the explaination a bit more clear, and fixed the "reference" idea

Can't take a reference to a lexical variable? Surely you jest. What happened when you tried it?

He wants a lexical variable because he wants a new hash at the start of each iteration of the loop. Pass that hash as a reference to the gather function (or better yet, just get the hash by having gather() return a reference).

Global variables are bad news, and that's why this thread exists. :)

--
brian d foy <brian@stonehenge.com>