Your immediate problem is that perl interprets your %{ as a hash slice (see http://docstore.mik.ua/orelly/perl/learn/ch05_05.htm for a small example)

Your larger problem is that you want to use a technique that is a relict from perl4 days and only (if at all) suitable for quick hacks

Instead of using

my %{"platform_$site"};
${"platform_$site"}{"thingy"}= 5;
foreach my $x ( keys %{"platform_$site"}) {
  ...
[download]

my %platform;
$platform{$site}{"thingy"}= 5;
foreach my $x ( keys %{$platform{$site}}) {
  ...
[download]

You can use the same technique for your arrays as well, i.e. use a so called HashOfArrays:

push @{$platform{$site}}, 1,2;
$platform{$site}[5]= 5;
foreach my $x ( @{$platform{$site}}) {
  ..
[download]

PS: I also notice you don't use 'use warnings;' and 'use strict;' at the beginning of your script. It is highly advisable to include those two lines. Avoids many bug finding sessions later.

Thanks for your reply.

Yes usually I include strict, but I had just taken an extract of an old script I'm patching to work on that particular function.

I also agree multidimensional arrays are probably the way to go, but if possible I'd rather keep the current variables as they are used throughout the other script.

Your immediate problem is that perl interprets your %{ as a hash slice

Is this for real?

It was the best explanation I could find at the moment. But I didn't check with deparse or something.

is it?

Let's rule out the fact that this deals with symbolic references, strict tells us ...

use strict;
use warnings;

{   no strict "refs";
    my $site = "foo";
    my @{"platforms_$site"} = qw( foo bar );
    my %{"platforms_$site"} = map { $_ => 1 } @{"platforms_$site"};
    }

=>

Can't declare array dereference in "my" at xx.pl line 8, near "} ="
Execution of xx.pl aborted due to compilation errors.
[download]

The difference is in the assignment part. You cannot use my there. When you drop those, you get:

use strict;
use warnings;

{   no strict "refs";
    my $site = "foo";
    @{"platforms_$site"} = qw( foo bar );
    %{"platforms_$site"} = map { $_ => 1 } @{"platforms_$site"};
    }
[download]

Which is still bad coding style, but this works.


Enjoy, Have FUN! H.Merijn

Hash (and array) slices always start with @. No slices start with %.

my %{"$name"};
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is the same as

my %{$name}
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which is the same as

my %$name;  # Symbolic dereference
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which no more works than

my %$ref;   # Generic deference
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Don't go that road. Please. Done that, been there. It leads to unwanted things, in the widest sense of "unwanted". Really!

Symbolic reference (where the name of the hash/array/scalar is in a variable name) can always be made strict and safer by embedding it inside a hash:

my $hash_name = "platform_$site";
%$hash_name = ( key => $value );
:
my $value = ${$hash_name}{key};
[download]

=>

my %global_hash;
my $hash_name = "platform_$site";
$global_hash{$hash_name} = { key => $value };
:
my $value = $global_hash{$hash_name}{key};
[download]

Or - even better - go with jethro's suggestion to use multidimensional data structures.

...ditto...but once you've touched some code, you own it, and anything it may or may not do with good or bad data as input. so as much as this sounds as a bit of a pain, you're much better of re-writing the code to use good/clean programming patterns. code with symbolic reference variables is harder to debug/maintain/improve. i once wrote a data reporting perl script initially (and naively) using symbolic reference variables. i immediately re-wrote it using multilevel hashes, and the spaghetti code turned magically into nicely ordered simple subroutines and loops, and halved the number of lines of code.
the hardest line to type correctly is: stty erase ^H