Help with an regular expression matching multiple lines

I'm working on a file with a format somewhat like this:

<price>
<list>1</list>
<country>CAD</country>
</price>
<price>
<list>2</list>
<country>USD</country>
</price>
<price>
<list>3</list>
<country>CAD</country>
</price>

I need an expression that will delete the <price>..</price> composites that don't have USD in them.

The closest I was able to get was this:

$/="";
if (/<price>/../<\/price>/){s/<price>.*?<list>.*?<\/list>.*?<country>CAD<\/country>.*?<\/price>//s}

It would delete the top composite, but it would leave the other CAD on the bottom ... and the line isn't very robust because additional lines with different values just deletes everything.
hadronsAsked:
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ozoConnect With a Mentor Commented:
$_='
<price>
<list>1</list>
<country>CAD</country>
</price>
<price>
<list>2</list>
<country>USD</country>
</price>
<price>
<list>3</list>
<country>CAD</country>
</price>
';
s#<price>((?!USD).)*</price>##sg;
print;
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wilcoxonCommented:
Whenever processing XML, you should really, REALLY use an XML processing module - at least XML::Simple if not XML::LibXML, XML::Twig, XML::SAX (my current favorite) or one of the others.
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hadronsAuthor Commented:
Actually wilcoxon, I am using XML:Twig, but I've found that i still have to re-edit the files because the data itself is so dirty and I haven't found a good way to prevent node A from printing if node B has a certain value.

ozo, the expression is very close to what I need, but the expression is taking too big a chunk of data because other data that's in between the price composites is being consolidated and deleted too.
0
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ozoCommented:
Can you give an example of data for which the expression does not work, along with an example of what you would want the result to be?
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Terry WoodsConnect With a Mentor IT GuruCommented:
Try adding a ? character to ozo's pattern as follows:
s#<price>((?!USD).)*?</price>##sg;

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Edit: On further thought, that probably won't help!
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hadronsAuthor Commented:
ozo, here's a better example of what I was looking for (my first example wasn't very good):

The file starts like this;

<product>
<price>
<list>1</list>
<country>CAD</country>
</price>
</product>

<product>
<price>
<list>2</list>
<country>CAD</country>
</price>
<price>
<list>2</list>
<country>USD</country>
</price>
</product>

<product>
<price>
<list>2</list>
<country>USD</country>
</price>
<price>
<list>3</list>
<country>CAD</country>
</price>
</product>

And to end up with this:

<product>
</product>

<product>
<price>
<list>2</list>
<country>USD</country>
</price>
</product>

<product>
<price>
<list>2</list>
<country>USD</country>
</price>
</product>
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Derek JensenCommented:
@Terry, don't doubt yourself! ;-) This seemed to work fine for me:

s#<price>((?!USD).+?)</price>##sg;
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ozoCommented:
Other than a small difference in white space, the modification in http:#a39676531 does seem to produce the desired result on the example of http:#a39676632
It may also be conceivable that
s#<price>((?!USD|</price>).)*</price>\s*##sg;
could work better in some circumstances.
0
 
hadronsAuthor Commented:
Thank you all ... when I saw Terry's edited comment I didn't try using the non-greedy match, but it worked perfectly
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