Perl: Hash within Array within Hash - arrays

Question

I am trying to build a Hash that has an array as one value; this array will then contain hashes. Unfortunately, I have coded it wrong and it is being interpreted as a psuedo-hash. Please help!
my $xcHash = {};
my $xcLine;
#populate hash header
$xcHash->{XC_HASH_LINES} = ();
#for each line of data
$xcLine = {};
#populate line hash
push(#{$xcHash->{XC_HASH_LINES}}, $xcLine);
foreach $xcLine ($xcHash->{XC_HASH_LINES})
#psuedo-hash error occurs when I try to use $xcLine->{...}

Answer 1

$xcHash->{XC_HASH_LINES} is an arrayref and not an array. So
$xcHash->{XC_HASH_LINES} = ();
should be:
$xcHash->{XC_HASH_LINES} = [];
foreach takes a list. It can be a list containing a single scalar (foreach ($foo)), but that's not what you want here.
foreach $xcLine ($xcHash->{XC_HASH_LINES})
should be:
foreach my $xcLine (#{$xcHash->{XC_HASH_LINES}})

Answer 2

foreach $xcLine ($xcHash->{XC_HASH_LINES})
should be
foreach $xcLine ( #{ $xcHash->{XC_HASH_LINES} } )
See http://perlmonks.org/?node=References+quick+reference for easy to remember rules for how to dereference complex data structures.

Answer 3

Golden Rule #1
use strict;
use warnings;
It might seem like a fight at the beginning, but they will instill good Perl practices and help identify many syntactical errors that might otherwise go unnoticed.
Also, Perl has a neat feature called autovivification. It means that $xcHash and $xcLine need not be pre-defined or constructed as references to arrays or hashes.
The issue faced here is to do with the not uncommon notion that a scalar can hold an array or hash; it doesn't. What it holds is a reference. This means that the $xcHash->{XC_HASH_LINES} is an arrayref, not an array, which is why it needs to be dereferenced as an array using the #{...} notation.

Answer 4

Here's what I would do:
my %xcHash;
for each line of data:
push #{$xcHash{XC_HASH_LINES}},$xcLine;