How do I create an XML file (in a specific location), containing a given hash?

Question

So I have a simple hash key=>{value} and I need to output this in an XML file (in a specific location).

The output should be like this:

<keys> <key1> <value1> </value1> </key1> </keys>

I searched on other forums and found that xml::Simple would be a solution, but new in Perl.

So what are you asking then? Not how to construct XML (since that part is ‘*imaginary*’)… — Biffen, Feb 03 '16 at 11:39
You're going to have to provide *a lot* more details. What's the format of the XML? What have you tried? What doesn't work? Please read [**this**](http://stackoverflow.com/help/how-to-ask). — Biffen, Feb 03 '16 at 11:46
How many (logical) formats can you have, if i told you that i have a key->value hash — user30771, Feb 03 '16 at 11:48
Infinite! What should the XML look like?! Show us an example! — Biffen, Feb 03 '16 at 11:50
So nothing like what you've showed us in your question? Put that *in the question*, where it should have been in the first place. And while you do, add your code, and a clear description of how it doesn't work. — Biffen, Feb 03 '16 at 11:54
Also - if it's key-value, are you sure you want XML? XML is pretty heavy, and JSON may be more appropriate. — Sobrique, Feb 03 '16 at 13:41

ikegami · Accepted Answer · 2016-02-03T15:34:55.363

XML::Simple is abysmal, especially for generating XML.

You said the format should be the following:

<keys>
   <key1><value1></value1></key1>
   [...]
</keys>

That format doesn't make much sense. The solution below produces XML in the following format:

<elements>
   <element><key>key1</key><value>value1</value></element>
   [...]
</elements>

Solution:

use XML::Writer qw( );

open(my $fh, '>', $qfn)
   or die("Can't create \"$qfn\": $!\n");

my $writer = XML::Writer->new(OUTPUT => $fh);
$writer->xmlDecl();
$writer->startTag("elements");
for my $key (sort keys(%hash)) {
   $writer->startTag("element");
   $writer->dataElement("key", $key);
   $writer->dataElement("value", $hash{$key});
   $writer->endTag("element");
}
$writer->endTag("keys");
$writer->end();

The following is a terser format:

<elements>
   <element key="key1">value1</element>
   [...]
</elements>

Solution:

use XML::Writer qw( );

open(my $fh, '>', $qfn)
   or die("Can't create \"$qfn\": $!\n");

my $writer = XML::Writer->new(OUTPUT => $fh);
$writer->xmlDecl();
$writer->startTag("elements");
for my $key (sort keys(%hash)) {
   $writer->dataElement("element", $hash{$key}, key => $key);
}
$writer->endTag("keys");
$writer->end();

Adjust at will.

Thank youvery much for all the efort. I think I'll go with the second solution. — user30771, Feb 03 '16 at 12:54

score 0 · Answer 2 · edited May 23 '17 at 10:28

ikegami has covered the hash -> XML case quite nicely. I wish to offer an alternative suggestion - don't, use JSON instead. XML is quite powerful and complicated, but it's really designed as a document format - think how HTML does things - you have tags, attributes and content.

For a significant number of use cases, you're better off with JSON instead - it's a simpler format of hashes and arrays. As a result, it more directly reflects the perl data types.

So you can do:

#!/usr/bin/env perl

use strict;
use warnings;

use JSON;

my %stuff = ( key => "value", 
              another_key => "another_value", 
              some_tags => [ "tag1", "tag2", "tag3" ] ); 

print to_json ( \%stuff, { pretty => 1 } );

This gives you:

{
   "key" : "value",
   "another_key" : "another_value",
   "some_tags" : [
      "tag1",
      "tag2",
      "tag3"
   ]
}

Or collapses it onto one line if you just to_json ( \%stuff );:

{"another_key":"another_value","key":"value","some_tags":["tag1","tag2","tag3"]}

Reading it back in is as simple as:

my $json_str =  to_json ( \%stuff );

my $json_object = from_json ( $json_str );
print Dumper \$json_object;

If all you need is hashes and arrays (and can do without XML attributes, xpath, XSLT processing) then this may be a better fit - I suggest it, because you indicate that you want to export a simple hash.

But in either case - don't use XML::Simple - it isn't simple at all.

How do I create an XML file (in a specific location), containing a given hash?

2 Answers2