Extracting and modifying XML with deep structure from Linux command line - xmlstarlet

Question

I would like to select and change a value in an XML file. I'm trying to use xmlstarlet for this.
I have this file
<?xml version='1.0' encoding='UTF-8'?>
<DeviceDescription xmlns="http://www.3s-software.com/schemas/DeviceDescription-1.0.xsd">
<House>
<Id>
<Number>1</Number>
</Id>
</House>
<Car>
<Id>
<Number>2</Number>
</Id>
</Car>
</DeviceDescription>
My problem is the xmlns= field which xmlstarlet is picky about. Without this field I can use
xmlstarlet sel -t -v '/Description/House/Id/Number' /tmp/x.xml
I found that I can use a default namespace like this, but that returns both Id's
xmlstarlet sel -t -m "//_:Id" -v '_:Number' /tmp/x.xml
How do I specify a full path?

Answer 1

To only match the House id, add it to the -m argument:
xml sel -t -m '//_:House/_:Id' -v '_:Number'
If you want to use the namespace, specify it with -N, e.g.:
xml sel -N ns="http://www.3s-software.com/schemas/DeviceDescription-1.0.xsd" \
-t -v 'ns:DeviceDescription/ns:House/ns:Id/ns:Number'
So to update the value:
xml ed -N ns="http://www.3s-software.com/schemas/DeviceDescription-1.0.xsd" \
-u 'ns:DeviceDescription/ns:House/ns:Id/ns:Number' -v 3
Output:
<?xml version="1.0" encoding="UTF-8"?>
<DeviceDescription xmlns="http://www.3s-software.com/schemas/DeviceDescription-1.0.xsd">
<House>
<Id>
<Number>3</Number>
</Id>
</House>
<Car>
<Id>
<Number>2</Number>
</Id>
</Car>
</DeviceDescription>