Parsing deep XML

FlanOSU has asked for the wisdom of the Perl Monks concerning the following question:

I have successfully run the basic XML parsing examples found around the internet, but when I try to apply it to my actual xml files, I am stumped.

I could use some assistance in learning how to access the lower levels of this XML tree. Here is some of the output from Dumper (hopefully this is legible):

$VAR1 = {
          'xmlns:xsi' => 'http://www.w3.org/2001/XMLSchema-instance',
          'ICD_Name' => 'MFU_icd',
          'ICD_Description' => {
                               'MsgData' => {
                                            'MsgDataRegion' => {
                                                               'Msg_Da
+ta' => {
                                                                      
+       'Array' => {
                                                                      
+                  'ArrayName' => 'MFU_ID',
                                                                      
+                  'NumOfArrayRepetitions' => '1',
                                                                      
+                  'StructureType' => [
                                                                      
+                                     {
                                                                      
+                                       'DataLine' => {
[download]

I am trying to read down to the DataLine level, but I can't even get it to output the top level. Here is my code:

#!/usr/bin/perl

# use module
use strict;
use XML::Simple;
use Data::Dumper;

# read XML file
my $xmlfile = "./GA_MFU_Get_Status.xml";
my $ref = eval { XMLin($xmlfile) };

# print entire output
print Dumper($ref);

foreach my $item (@{$ref->{ICD_Description}})
{
    print $item->{MsgData}, "\n";
    print ": ", $item->{MsgData}->{MsgDataRegion}->{Msg_Data}->{Array}
+, "\n"; 
    print ": ", $item->{MsgData}->{MsgDataRegion}->{Msg_Data}->{Array}
+->{StructureType}->{DataLine}, "\n";
    print ": ", $item->{MsgData}->{MsgDataRegion}->{Msg_Data}->{Array}
+->{StructureType}->{DataLine}->{DataField}, "\n"; 

    print "\n";
}
[download]

I get the message "Not an ARRAY reference at C:\GA_MFU_ICD_XML\XML\XMLparser.pl line 18." Anything to get my on the right track would be much appreciated.

Comment on Parsing deep XML Select or Download Code

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Re: Parsing deep XML by lostjimmy (Chaplain) on Feb 24, 2010 at 22:39 UTC
The error message is exactly what the problem is--you are trying to use the reference in `$ref->{ICD_Description}` as an array, when it's actually a hash. You can't use your `foreach` loop to traverse through the data in the way you are trying. In other words, `$ref` is a hashref, and `$ref->{ICD_Description}` is also a hashref, but you're trying to use it like it's an array ref. The output from Dumper is the key to seeing what kind of data are in the variable. If a section starts with a `{`, it is a hashref; if it starts with a `[` it is an array ref. It also looks like `StructureType` points to an array ref, which then has a list of hashrefs. You should be able to access the array of `StructureType`s with something similar to the following (untested): `foreach my $structure_type (@{$ref{ICD_Description}{MsgData}{MsgDataRe +gion}{Msg_Data}{Array}{StructureType}}) { print "$structure_type{DataLine}{DataField}\n"; }` [download]	[reply] [d/l] [select]
Re: Parsing deep XML by grantm (Parson) on Feb 25, 2010 at 03:22 UTC
Before you get too deep into using XML::Simple, take a look at this article which demonstrates how XML::LibXML can actually be simpler.	[reply]