By the way, in "Perl Best Practices" Damian Conway advises that you should always write 'my' before your for-loop variable because if you don't :

[The resulting] behaviour is contrary to all reasonable expectation.  Everywhere else in Perl, when you declare a lexical variable, it's visible throughout the remainder of its scope, unless another explicit my declaration hides it.  So it's natural to expect that the [variable] used in the for loop is the same lexical [variable] that was declared before the loop.

But it isn't.

My code makes it neccessary to loop through an array and to output all elements using a reference.

That doesn't seem to make a lot of sense:

use strict;
use warnings;
use 5.010;

my @arr = (10, 20, 30);

for my $num (@arr) {
    say ${\$num};
}


--output:--
10
20
30
[download]

$sref = \$string;
foreach $string ( @array_of_strings ) {
    print $sref, \$string, "\n";
}
[download]

Here is the effect when perl localizes a variable:

#Whoops.  An Anonymous Monk already posted a good example.

And because a for loop aliases each element in the array to the loop variable, changes to the loop variable change the elements of the array.

Why? I would have expected that using the foreach $string acutally is assigned to whatever is the element of the array but aparently this is not the case.

Turn on strict and warnings and you'll see why.

use warnings;
use strict;

my $sref = \$string;
foreach $string ( @array_of_strings ) {
    print $$sref;
}


$ perl sref_o.pl
Global symbol "$string" requires explicit package name at sref_o.pl li
+ne 4.
Global symbol "$string" requires explicit package name at sref_o.pl li
+ne 5.
Global symbol "@array_of_strings" requires explicit package name at sr
+ef_o.pl line 5.
Execution of sref_o.pl aborted due to compilation errors.
[download]

You don't need to be an utter cowdawg towards the OP -- strict and warnings are irrelevant to his issue.

I don't fully grok the semantics of foreach but I suspect the correct answer is as follows:

$sref = \$string sets $sref to point to the variable $string. All is well here. But then foreach enters the picture and localises $string -- this $string is only available to the inner loop. $sref continues pointing to the $string in the outer loop. Testing this without the string reference:

my $string = "I'm still here";
say $string;

my @array_of_strings = qw/foo bar baz quux/;

foreach $string ( @array_of_strings ) {
        say $string;
}
say $string;

# output
I'm still here
foo
bar
baz
quux
I'm still here
[download]

Yep, looks like what I described. Now, if you add the $sref, you'll notice it'll print the outer loop value for the whole time -- it points to the wrong $string.

Thanks for that answer.
Though quite some time has passed since I last read the corresponding paragraph in perldoc, I wouldn't have expected that the reference still points to the variable outside of the loop since it is used within the loop.

All variables have been previouly defined using my (i.e. in the beginning of the script).

You don't need to be an utter cowdawg towards the OP -- strict and warnings are irrelevant to his issue.

I wasn't being mean, ornery or cantankerous. Take what I said at face value. If strict and warnings were turned on (as I showed) the problem would have shown itself very clearly.

---

Peter L. Berghold -- Unix Professional
Peter -at- Berghold -dot- Net; AOL IM redcowdawg Yahoo IM: blue_cowdawg