http://www.perlmonks.org?node_id=337131

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

I'm trying to learn how to manipulate XML using Perl. I got this code off a website, but it isn't working. 
use strict;
use XML::Simple;

my $file = 'files/camelids.xml';
my $xs1 = XML::Simple->new();

my $doc = $xs1->XMLin($file);

foreach my $key (keys (%{$doc->{species}})){
   print $doc->{species}->{$key}->{'common-name'} . ' (' . $key . ') '
+;
   print $doc->{species}->{$key}->{conservation}->{status} . "\n";
}

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This is the file it's accessing... 
<?xml version="1.0"?>
<camelids>
  <species name="Camelus bactrianus">
    <common-name>Bactrian Camel</common-name>
    <physical-characteristics>
      <mass>450 to 500 kg.</mass>
      <appearance>
        The most noticeable ...
      </appearance>
    </physical-characteristics>
    <natural-history>
       <food-habits>
         Camels are herbivores...
       </food-habits>
       <reproduction>
         Mating season occurs ... 
       </reproduction>
       <behavior>
         Domestic camels ...
       </behavior>
       <habitat>
         The camel's habitat ...
       </habitat>
    </natural-history>
    <conservation status="endangered">
      <detail>
        Camels were thought ...
      </detail>
    </conservation>
  </species>
</camelids>

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Can anyone tell me what's wrong with it, or give me some kind of guidance on how to manipulate XML in Perl.

Sorry, by not working, I meant that it's totally and completely not working. I'm getting a "500 Internal Server Error" error.

Replies are listed 'Best First'.
Re: Perl and XML
by jeffa (Bishop) on Mar 16, 2004 at 23:08 UTC
    To elaborate on what bart said, you have to print out a Content Header if you want to view this as a web page from a browser. One easy way is to use CGI.pm: 
    use strict;
use XML::Simple;
use CGI qw(header);

print header('text/plain');

my $xs1 = XML::Simple->new();
my $doc = $xs1->XMLin('files/camelids.xml');

foreach my $key (keys (%{$doc->{species}})){
   print $doc->{species}->{$key}->{'common-name'} . " ($key) ";
   print $doc->{species}->{$key}->{conservation}->{status} . "\n";
}

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    You also have to make sure that the CGI file is executable by everyone ... "chmod 755 foo.cgi" should do the trick if you have command line access.

    jeffa

    L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)
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[d/l]
      thank you - got it, that was the problem
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Re: Perl and XML
by chip (Curate) on Mar 16, 2004 at 21:30 UTC
    When in doubt of a dada structure, use Data::Dumper, YAML, or the debugger's "x" command to see what it actually is. Then figuring out how to access it should be child's play.

        -- Chip Salzenberg, Free-Floating Agent of Chaos

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Re: Perl and XML
by bart (Canon) on Mar 16, 2004 at 22:54 UTC
    I'm getting a "500 Internal Server Error" error.
    Duh? You're running this as a CGI script? So where do you print out the header(s), and the blank line?

    Your syntax is fine, I don't have a sample of your XML file, and thus I'm not convinced that's not all there is to it.

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      what do you mean by header and blank line? 
      #!/usr/bin/perl

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      these things?
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[d/l]
        No, you need that too, and it must be a proper path to perl too, but that's usually called the shebang line.

        No, I'm now talking about CGI 101, you can use a simple 

        print "Content-type: text/plain\n\n";

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        before your print anything else, or something similar but more advanced from one of the CGI modules.

        For simple experimentation, it'd be best to use something like 

        use CGI::Carp 'fatalsToBrowser';

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        because then you'll get your Perl error messages in the browser window, too.
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[d/l]
[select]
Re: Perl and XML
by matija (Priest) on Mar 16, 2004 at 21:28 UTC
    First, I think you will need to access $doc->{camelids}{species}...etc... - the camelids needs to be explicitly there.

    Second, I warmly recommend you use XML::Smart.

    I've used both XML::Simple and XML::Smart, and working with Smart is much, much easier for me.

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[d/l]
      - the camelids needs to be explicitly there.

      No, with the default options the original script uses, the top level element will be discarded.

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Re: Perl and XML
by Anonymous Monk on Mar 16, 2004 at 22:56 UTC
    I played with XML::Simple a little and found out that it is really good for very simple things. If you are having trouble doing something that is less than simple you might try using XML::LibXML. LibXML is harder to get your head around as a beginner but it works really well.
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